diff --git a/src/common/audio/music/i_music.cpp b/src/common/audio/music/i_music.cpp
index d7460fc768..19c8309162 100644
--- a/src/common/audio/music/i_music.cpp
+++ b/src/common/audio/music/i_music.cpp
@@ -182,7 +182,7 @@ static void SetupGenMidi()
 	auto genmidi = fileSystem.ReadFile(lump);
 
 	if (genmidi.GetSize() < 8 + 175 * 36 || memcmp(genmidi.GetMem(), "#OPL_II#", 8)) return;
-	ZMusic_SetGenMidi((uint8_t*)genmidi.GetString() + 8);
+	ZMusic_SetGenMidi(genmidi.GetBytes() + 8);
 }
 
 static void SetupWgOpn()
diff --git a/src/common/engine/sc_man.cpp b/src/common/engine/sc_man.cpp
index 21a777756f..cc72273a18 100644
--- a/src/common/engine/sc_man.cpp
+++ b/src/common/engine/sc_man.cpp
@@ -200,8 +200,11 @@ void FScanner :: OpenLumpNum (int lump)
 {
 	Close ();
 	{
-		FileData mem = fileSystem.ReadFile(lump);
-		ScriptBuffer = mem.GetString();
+		auto mem = fileSystem.OpenFileReader(lump);
+		auto buff = ScriptBuffer.LockNewBuffer(mem.GetLength());
+		mem.Read(buff, mem.GetLength());
+		buff[mem.GetLength()] = 0;
+		ScriptBuffer.UnlockBuffer();
 	}
 	ScriptName = fileSystem.GetFileFullPath(lump).c_str();
 	LumpNum = lump;
diff --git a/src/common/rendering/gl/gl_shader.cpp b/src/common/rendering/gl/gl_shader.cpp
index 85ba5c1ebe..afa05b8630 100644
--- a/src/common/rendering/gl/gl_shader.cpp
+++ b/src/common/rendering/gl/gl_shader.cpp
@@ -375,11 +375,9 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 
 	int vp_lump = fileSystem.CheckNumForFullName(vert_prog_lump, 0);
 	if (vp_lump == -1) I_Error("Unable to load '%s'", vert_prog_lump);
-	FileData vp_data = fileSystem.ReadFile(vp_lump);
 
 	int fp_lump = fileSystem.CheckNumForFullName(frag_prog_lump, 0);
 	if (fp_lump == -1) I_Error("Unable to load '%s'", frag_prog_lump);
-	FileData fp_data = fileSystem.ReadFile(fp_lump);
 
 
 
@@ -410,8 +408,8 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 	vp_comb << "#line 1\n";
 	fp_comb << "#line 1\n";
 
-	vp_comb << RemoveLayoutLocationDecl(vp_data.GetString(), "out").GetChars() << "\n";
-	fp_comb << RemoveLayoutLocationDecl(fp_data.GetString(), "in").GetChars() << "\n";
+	vp_comb << RemoveLayoutLocationDecl(GetStringFromLump(vp_lump), "out").GetChars() << "\n";
+	fp_comb << RemoveLayoutLocationDecl(GetStringFromLump(fp_lump), "in").GetChars() << "\n";
 	FString placeholder = "\n";
 
 	if (proc_prog_lump != NULL)
@@ -423,7 +421,7 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 			int pp_lump = fileSystem.CheckNumForFullName(proc_prog_lump, 0);	// if it's a core shader, ignore overrides by user mods.
 			if (pp_lump == -1) pp_lump = fileSystem.CheckNumForFullName(proc_prog_lump);
 			if (pp_lump == -1) I_Error("Unable to load '%s'", proc_prog_lump);
-			FString pp_data = fileSystem.ReadFile(pp_lump).GetString();
+			FString pp_data = GetStringFromLump(pp_lump);
 
 			if (pp_data.IndexOf("ProcessMaterial") < 0 && pp_data.IndexOf("SetupMaterial") < 0)
 			{
@@ -433,15 +431,13 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 				{
 					int pl_lump = fileSystem.CheckNumForFullName("shaders/glsl/func_defaultmat2.fp", 0);
 					if (pl_lump == -1) I_Error("Unable to load '%s'", "shaders/glsl/func_defaultmat2.fp");
-					FileData pl_data = fileSystem.ReadFile(pl_lump);
-					fp_comb << "\n" << pl_data.GetString();
+					fp_comb << "\n" << GetStringFromLump(pl_lump);
 				}
 				else
 				{
 					int pl_lump = fileSystem.CheckNumForFullName("shaders/glsl/func_defaultmat.fp", 0);
 					if (pl_lump == -1) I_Error("Unable to load '%s'", "shaders/glsl/func_defaultmat.fp");
-					FileData pl_data = fileSystem.ReadFile(pl_lump);
-					fp_comb << "\n" << pl_data.GetString();
+					fp_comb << "\n" << GetStringFromLump(pl_lump);
 
 					if (pp_data.IndexOf("ProcessTexel") < 0)
 					{
@@ -467,8 +463,7 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 			{
 				int pl_lump = fileSystem.CheckNumForFullName("shaders/glsl/func_defaultlight.fp", 0);
 				if (pl_lump == -1) I_Error("Unable to load '%s'", "shaders/glsl/func_defaultlight.fp");
-				FileData pl_data = fileSystem.ReadFile(pl_lump);
-				fp_comb << "\n" << pl_data.GetString();
+				fp_comb << "\n" << GetStringFromLump(pl_lump);
 			}
 
 			// ProcessMaterial must be considered broken because it requires the user to fill in data they possibly cannot know all about.
@@ -490,8 +485,7 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 	{
 		int pp_lump = fileSystem.CheckNumForFullName(light_fragprog, 0);
 		if (pp_lump == -1) I_Error("Unable to load '%s'", light_fragprog);
-		FileData pp_data = fileSystem.ReadFile(pp_lump);
-		fp_comb << pp_data.GetString() << "\n";
+		fp_comb << GetStringFromLump(pp_lump) << "\n";
 	}
 
 	if (gl.flags & RFL_NO_CLIP_PLANES)
diff --git a/src/common/rendering/gl/gl_shaderprogram.cpp b/src/common/rendering/gl/gl_shaderprogram.cpp
index 69729a8c7a..feca86aa89 100644
--- a/src/common/rendering/gl/gl_shaderprogram.cpp
+++ b/src/common/rendering/gl/gl_shaderprogram.cpp
@@ -28,6 +28,7 @@
 #include "hw_shaderpatcher.h"
 #include "filesystem.h"
 #include "printf.h"
+#include "cmdlib.h"
 
 namespace OpenGLRenderer
 {
@@ -88,7 +89,9 @@ void FShaderProgram::Compile(ShaderType type, const char *lumpName, const char *
 {
 	int lump = fileSystem.CheckNumForFullName(lumpName);
 	if (lump == -1) I_FatalError("Unable to load '%s'", lumpName);
-	FString code = fileSystem.ReadFile(lump).GetString();
+	auto sp = fileSystem.ReadFile(lump);
+	FString code = GetStringFromLump(lump);
+
 	Compile(type, lumpName, code, defines, maxGlslVersion);
 }
 
diff --git a/src/common/rendering/gles/gles_shader.cpp b/src/common/rendering/gles/gles_shader.cpp
index 16ff0eb65c..8f9103c610 100644
--- a/src/common/rendering/gles/gles_shader.cpp
+++ b/src/common/rendering/gles/gles_shader.cpp
@@ -410,8 +410,8 @@ bool FShader::Load(const char * name, const char * vert_prog_lump_, const char *
 	vp_comb << "#line 1\n";
 	fp_comb << "#line 1\n";
 
-	vp_comb << RemoveLayoutLocationDecl(vp_data.GetString(), "out").GetChars() << "\n";
-	fp_comb << RemoveLayoutLocationDecl(fp_data.GetString(), "in").GetChars() << "\n";
+	vp_comb << RemoveLayoutLocationDecl(GetStringFromLump(vp_lump), "out").GetChars() << "\n";
+	fp_comb << RemoveLayoutLocationDecl(GetStringFromLump(fp_lump), "in").GetChars() << "\n";
 	FString placeholder = "\n";
 
 	if (proc_prog_lump.Len())
@@ -422,7 +422,8 @@ bool FShader::Load(const char * name, const char * vert_prog_lump_, const char *
 		{
 			int pp_lump = fileSystem.CheckNumForFullName(proc_prog_lump);
 			if (pp_lump == -1) I_Error("Unable to load '%s'", proc_prog_lump.GetChars());
-			FString pp_data = fileSystem.ReadFile(pp_lump).GetString();
+			auto ppf = fileSystem.ReadFile(pp_lump);
+			FString pp_data = GetStringFromLump(pp_lump);
 
 			if (pp_data.IndexOf("ProcessMaterial") < 0 && pp_data.IndexOf("SetupMaterial") < 0)
 			{
@@ -432,15 +433,13 @@ bool FShader::Load(const char * name, const char * vert_prog_lump_, const char *
 				{
 					int pl_lump = fileSystem.CheckNumForFullName("shaders_gles/glsl/func_defaultmat2.fp", 0);
 					if (pl_lump == -1) I_Error("Unable to load '%s'", "shaders_gles/glsl/func_defaultmat2.fp");
-					FileData pl_data = fileSystem.ReadFile(pl_lump);
-					fp_comb << "\n" << pl_data.GetString();
+					fp_comb << "\n" << GetStringFromLump(pl_lump);
 				}
 				else
 				{
 					int pl_lump = fileSystem.CheckNumForFullName("shaders_gles/glsl/func_defaultmat.fp", 0);
 					if (pl_lump == -1) I_Error("Unable to load '%s'", "shaders_gles/glsl/func_defaultmat.fp");
-					FileData pl_data = fileSystem.ReadFile(pl_lump);
-					fp_comb << "\n" << pl_data.GetString();
+					fp_comb << "\n" << GetStringFromLump(pl_lump);
 
 					if (pp_data.IndexOf("ProcessTexel") < 0)
 					{
@@ -466,8 +465,7 @@ bool FShader::Load(const char * name, const char * vert_prog_lump_, const char *
 			{
 				int pl_lump = fileSystem.CheckNumForFullName("shaders_gles/glsl/func_defaultlight.fp", 0);
 				if (pl_lump == -1) I_Error("Unable to load '%s'", "shaders_gles/glsl/func_defaultlight.fp");
-				FileData pl_data = fileSystem.ReadFile(pl_lump);
-				fp_comb << "\n" << pl_data.GetString();
+				fp_comb << "\n" << GetStringFromLump(pl_lump);
 			}
 
 			// ProcessMaterial must be considered broken because it requires the user to fill in data they possibly cannot know all about.
@@ -489,8 +487,7 @@ bool FShader::Load(const char * name, const char * vert_prog_lump_, const char *
 	{
 		int pp_lump = fileSystem.CheckNumForFullName(light_fragprog, 0);
 		if (pp_lump == -1) I_Error("Unable to load '%s'", light_fragprog.GetChars());
-		FileData pp_data = fileSystem.ReadFile(pp_lump);
-		fp_comb << pp_data.GetString() << "\n";
+		fp_comb << GetStringFromLump(pp_lump) << "\n";
 	}
 
 	if (gles.flags & RFL_NO_CLIP_PLANES)
diff --git a/src/common/rendering/gles/gles_shaderprogram.cpp b/src/common/rendering/gles/gles_shaderprogram.cpp
index 8677257f33..289008c219 100644
--- a/src/common/rendering/gles/gles_shaderprogram.cpp
+++ b/src/common/rendering/gles/gles_shaderprogram.cpp
@@ -26,6 +26,7 @@
 #include "hw_shaderpatcher.h"
 #include "filesystem.h"
 #include "printf.h"
+#include "cmdlib.h"
 
 namespace OpenGLESRenderer
 {
@@ -88,7 +89,8 @@ void FShaderProgram::Compile(ShaderType type, const char *lumpName, const char *
 {
 	int lump = fileSystem.CheckNumForFullName(lumpName);
 	if (lump == -1) I_FatalError("Unable to load '%s'", lumpName);
-	FString code = fileSystem.ReadFile(lump).GetString();
+	auto sp = fileSystem.ReadFile(lump);
+	FString code = GetStringFromLump(lump);
 	Compile(type, lumpName, code, defines, maxGlslVersion);
 }
 
diff --git a/src/common/rendering/vulkan/shaders/vk_ppshader.cpp b/src/common/rendering/vulkan/shaders/vk_ppshader.cpp
index f83b01c938..d9f6078c73 100644
--- a/src/common/rendering/vulkan/shaders/vk_ppshader.cpp
+++ b/src/common/rendering/vulkan/shaders/vk_ppshader.cpp
@@ -26,6 +26,7 @@
 #include "zvulkan/vulkanbuilders.h"
 #include "vulkan/system/vk_commandbuffer.h"
 #include "filesystem.h"
+#include "cmdlib.h"
 
 VkPPShader::VkPPShader(VulkanRenderDevice* fb, PPShader *shader) : fb(fb)
 {
@@ -66,7 +67,8 @@ FString VkPPShader::LoadShaderCode(const FString &lumpName, const FString &defin
 {
 	int lump = fileSystem.CheckNumForFullName(lumpName);
 	if (lump == -1) I_FatalError("Unable to load '%s'", lumpName.GetChars());
-	FString code = fileSystem.ReadFile(lump).GetString();
+	auto sp = fileSystem.ReadFile(lump);
+	FString code = GetStringFromLump(lump);
 
 	FString patchedCode;
 	patchedCode.AppendFormat("#version %d\n", 450);
diff --git a/src/common/rendering/vulkan/shaders/vk_shader.cpp b/src/common/rendering/vulkan/shaders/vk_shader.cpp
index 2c3eb9241b..3784543b33 100644
--- a/src/common/rendering/vulkan/shaders/vk_shader.cpp
+++ b/src/common/rendering/vulkan/shaders/vk_shader.cpp
@@ -466,8 +466,7 @@ FString VkShaderManager::LoadPublicShaderLump(const char *lumpname)
 	int lump = fileSystem.CheckNumForFullName(lumpname, 0);
 	if (lump == -1) lump = fileSystem.CheckNumForFullName(lumpname);
 	if (lump == -1) I_Error("Unable to load '%s'", lumpname);
-	FileData data = fileSystem.ReadFile(lump);
-	return data.GetString();
+	return GetStringFromLump(lump);
 }
 
 FString VkShaderManager::LoadPrivateShaderLump(const char *lumpname)
@@ -475,7 +474,7 @@ FString VkShaderManager::LoadPrivateShaderLump(const char *lumpname)
 	int lump = fileSystem.CheckNumForFullName(lumpname, 0);
 	if (lump == -1) I_Error("Unable to load '%s'", lumpname);
 	FileData data = fileSystem.ReadFile(lump);
-	return data.GetString();
+	return GetStringFromLump(lump);
 }
 
 VkPPShader* VkShaderManager::GetVkShader(PPShader* shader)
diff --git a/src/common/scripting/interface/vmnatives.cpp b/src/common/scripting/interface/vmnatives.cpp
index 636c340ae6..3e75e75d8a 100644
--- a/src/common/scripting/interface/vmnatives.cpp
+++ b/src/common/scripting/interface/vmnatives.cpp
@@ -841,7 +841,7 @@ DEFINE_ACTION_FUNCTION(_Wads, ReadLump)
 	PARAM_PROLOGUE;
 	PARAM_INT(lump);
 	const bool isLumpValid = lump >= 0 && lump < fileSystem.GetNumEntries();
-	ACTION_RETURN_STRING(isLumpValid ? fileSystem.ReadFile(lump).GetString() : "");
+	ACTION_RETURN_STRING(isLumpValid ? GetStringFromLump(lump) : FString());
 }
 
 //==========================================================================
diff --git a/src/common/textures/animlib.cpp b/src/common/textures/animlib.cpp
index 949027786a..1b31244f30 100644
--- a/src/common/textures/animlib.cpp
+++ b/src/common/textures/animlib.cpp
@@ -217,7 +217,7 @@ static inline void drawframe(anim_t *anim, uint16_t framenumber)
 }
 
 // <length> is the file size, for consistency checking.
-int32_t ANIM_LoadAnim(anim_t *anim, uint8_t *buffer, size_t length)
+int32_t ANIM_LoadAnim(anim_t *anim, const uint8_t *buffer, size_t length)
 {
 	if (memcmp(buffer, "LPF ", 4)) return -1;
 
diff --git a/src/common/textures/animlib.h b/src/common/textures/animlib.h
index 1fdaa354fd..26fa124f40 100644
--- a/src/common/textures/animlib.h
+++ b/src/common/textures/animlib.h
@@ -92,7 +92,7 @@ struct anim_t
 	lp_descriptor * curlp;        // header of large page currently in memory
 	uint16_t * thepage;     // buffer where current large page is loaded
 	uint8_t imagebuffer[IMAGEBUFFERSIZE]; // buffer where anim frame is decoded
-	uint8_t * buffer;
+	const uint8_t * buffer;
 	uint8_t pal[768];
 	int32_t currentframe;
 };
@@ -105,7 +105,7 @@ struct anim_t
 //
 //****************************************************************************
 
-int32_t ANIM_LoadAnim(anim_t *anim, uint8_t *buffer, size_t length);
+int32_t ANIM_LoadAnim(anim_t *anim, const uint8_t *buffer, size_t length);
 
 //****************************************************************************
 //
diff --git a/src/common/textures/formats/anmtexture.cpp b/src/common/textures/formats/anmtexture.cpp
index f4fb332f0d..f57b0e31e6 100644
--- a/src/common/textures/formats/anmtexture.cpp
+++ b/src/common/textures/formats/anmtexture.cpp
@@ -104,7 +104,7 @@ FAnmTexture::FAnmTexture (int lumpnum, int w, int h)
 void FAnmTexture::ReadFrame(uint8_t *pixels, uint8_t *palette)
 {
 	FileData lump = fileSystem.ReadFile (SourceLump);
-	uint8_t *source = (uint8_t *)lump.GetMem(); 
+	auto source = lump.GetBytes(); 
 
 	anim_t anim;
 	if (ANIM_LoadAnim(&anim, source, (int)lump.GetSize()) >= 0)
diff --git a/src/common/utility/cmdlib.cpp b/src/common/utility/cmdlib.cpp
index 1e906e69c6..b5ac83415e 100644
--- a/src/common/utility/cmdlib.cpp
+++ b/src/common/utility/cmdlib.cpp
@@ -36,6 +36,7 @@
 
 #include "cmdlib.h"
 #include "fs_findfile.h"
+#include "filesystem.h"
 #include "files.h"
 #include "md5.h"
 
@@ -1008,3 +1009,17 @@ void uppercopy(char* to, const char* from)
 		to[i] = 0;
 }
 
+//==========================================================================
+//
+// GetStringFromLump
+//
+// Loads a zero terminated string from a lump in the file system
+//==========================================================================
+
+FString GetStringFromLump(int lump)
+{
+	FileData fd = fileSystem.ReadFile(lump);
+	FString ScriptBuffer(fd.GetString(), fd.GetSize());
+	ScriptBuffer.Truncate(strlen(ScriptBuffer.GetChars()));	// this is necessary to properly truncate the generated string to not contain 0 bytes.
+	return ScriptBuffer;
+}
diff --git a/src/common/utility/cmdlib.h b/src/common/utility/cmdlib.h
index e2e4aadbd0..9d94d0d3f2 100644
--- a/src/common/utility/cmdlib.h
+++ b/src/common/utility/cmdlib.h
@@ -87,6 +87,7 @@ struct MD5Context;
 
 void md5Update(FileReader& file, MD5Context& md5, unsigned len);
 void uppercopy(char* to, const char* from);
+FString GetStringFromLump(int lump);
 
 inline void fillshort(void* buff, size_t count, uint16_t clear)
 {
diff --git a/src/common/utility/palette.cpp b/src/common/utility/palette.cpp
index 7598f5d4ef..178db734b5 100644
--- a/src/common/utility/palette.cpp
+++ b/src/common/utility/palette.cpp
@@ -681,8 +681,8 @@ FString V_GetColorStringByName(const char* name, FScriptPosition* sc)
 	}
 
 	auto rgbNames = fileSystem.ReadFile(rgblump);
-	rgb = (char*)rgbNames.GetMem();
-	rgbEnd = rgb + fileSystem.FileLength(rgblump);
+	rgb = rgbNames.GetString();
+	rgbEnd = rgb + rgbNames.GetSize();
 	step = 0;
 	namelen = strlen(name);
 
diff --git a/src/gamedata/keysections.cpp b/src/gamedata/keysections.cpp
index 390c8009f8..8561b6b247 100644
--- a/src/gamedata/keysections.cpp
+++ b/src/gamedata/keysections.cpp
@@ -166,8 +166,8 @@ void D_LoadWadSettings ()
 	while ((lump = fileSystem.FindLump ("KEYCONF", &lastlump)) != -1)
 	{
 		FileData data = fileSystem.ReadFile (lump);
-		const char *eof = data.GetString() + fileSystem.FileLength (lump);
-		const char *conf = data.GetString();
+		const char* conf = data.GetString();
+		const char *eof = conf + data.GetSize();
 
 		while (conf < eof)
 		{
diff --git a/src/gamedata/xlat/parsecontext.cpp b/src/gamedata/xlat/parsecontext.cpp
index 1810af55dc..0caa72f4b2 100644
--- a/src/gamedata/xlat/parsecontext.cpp
+++ b/src/gamedata/xlat/parsecontext.cpp
@@ -323,12 +323,12 @@ void FParseContext::ParseLump(const char *lumpname)
 	}
 
 	// Read the lump into a buffer and add a 0-terminator
-	auto lumpdata = fileSystem.ReadFile(lumpno);
 
 	SourceLine = 0;
 	SourceFile = lumpname;
 
-	const char *sourcep = lumpdata.GetString();
+	FString source = GetStringFromLump(lumpno);
+	const char *sourcep = source.GetChars();
 	while ( (tokentype = GetToken(sourcep, &token)) )
 	{
 		// It is much easier to handle include statements outside the main parser.
diff --git a/src/intermission/intermission_parse.cpp b/src/intermission/intermission_parse.cpp
index 5b2de2c4db..b5a51aab58 100644
--- a/src/intermission/intermission_parse.cpp
+++ b/src/intermission/intermission_parse.cpp
@@ -320,7 +320,7 @@ bool FIntermissionActionTextscreen::ParseKey(FScanner &sc)
 				}
 			}
 			if (!done)
-				mText = fileSystem.ReadFile(lump).GetString();
+				mText = GetStringFromLump(lump);
 		}
 		else
 		{
@@ -864,7 +864,7 @@ DIntermissionController* F_StartFinale (const char *music, int musicorder, int c
 			int lump = fileSystem.CheckNumForFullName(text, true);
 			if (lump > 0)
 			{
-				textscreen->mText = fileSystem.ReadFile(lump).GetString();
+				textscreen->mText = GetStringFromLump(lump);
 			}
 			else
 			{
diff --git a/src/maploader/glnodes.cpp b/src/maploader/glnodes.cpp
index 15b4b46ba8..a72b3b7e47 100644
--- a/src/maploader/glnodes.cpp
+++ b/src/maploader/glnodes.cpp
@@ -754,7 +754,7 @@ static int FindGLNodesInWAD(int labellump)
 				if (fileSystem.GetFileContainer(lump)==wadfile)
 				{
 					FileData mem = fileSystem.ReadFile(lump);
-					if (MatchHeader(fileSystem.GetFileFullName(labellump), mem.GetString())) return lump;
+					if (MatchHeader(fileSystem.GetFileFullName(labellump), GetStringFromLump(lump))) return lump;
 				}
 			}
 		}