diff --git a/src/common/audio/music/i_music.cpp b/src/common/audio/music/i_music.cpp
index 9a8ddfe81e..d7460fc768 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().GetChars() + 8);
+	ZMusic_SetGenMidi((uint8_t*)genmidi.GetString() + 8);
 }
 
 static void SetupWgOpn()
diff --git a/src/common/filesystem/filesystem.h b/src/common/filesystem/filesystem.h
index 97eece8023..febb769114 100644
--- a/src/common/filesystem/filesystem.h
+++ b/src/common/filesystem/filesystem.h
@@ -35,9 +35,9 @@ public:
 	FileData (const FileData &copy);
 	FileData &operator= (const FileData &copy);
 	~FileData ();
-	void *GetMem () { return Block.Len() == 0 ? NULL : (void *)Block.GetChars(); }
+	const void *GetMem () { return Block.Len() == 0 ? NULL : (void *)Block.GetChars(); }
 	size_t GetSize () { return Block.Len(); }
-	const FString &GetString () const { return Block; }
+	const char* GetString () const { return Block.GetChars(); }
 
 private:
 	FileData (const FString &source);
diff --git a/src/common/rendering/gl/gl_shader.cpp b/src/common/rendering/gl/gl_shader.cpp
index d1b6aee546..85ba5c1ebe 100644
--- a/src/common/rendering/gl/gl_shader.cpp
+++ b/src/common/rendering/gl/gl_shader.cpp
@@ -423,27 +423,27 @@ 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);
-			FileData pp_data = fileSystem.ReadFile(pp_lump);
+			FString pp_data = fileSystem.ReadFile(pp_lump).GetString();
 
-			if (pp_data.GetString().IndexOf("ProcessMaterial") < 0 && pp_data.GetString().IndexOf("SetupMaterial") < 0)
+			if (pp_data.IndexOf("ProcessMaterial") < 0 && pp_data.IndexOf("SetupMaterial") < 0)
 			{
 				// this looks like an old custom hardware shader.
 
-				if (pp_data.GetString().IndexOf("GetTexCoord") >= 0)
+				if (pp_data.IndexOf("GetTexCoord") >= 0)
 				{
 					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().GetChars();
+					fp_comb << "\n" << pl_data.GetString();
 				}
 				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().GetChars();
+					fp_comb << "\n" << pl_data.GetString();
 
-					if (pp_data.GetString().IndexOf("ProcessTexel") < 0)
+					if (pp_data.IndexOf("ProcessTexel") < 0)
 					{
 						// this looks like an even older custom hardware shader.
 						// We need to replace the ProcessTexel call to make it work.
@@ -452,7 +452,7 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 					}
 				}
 
-				if (pp_data.GetString().IndexOf("ProcessLight") >= 0)
+				if (pp_data.IndexOf("ProcessLight") >= 0)
 				{
 					// The ProcessLight signatured changed. Forward to the old one.
 					fp_comb << "\nvec4 ProcessLight(vec4 color);\n";
@@ -460,19 +460,19 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 				}
 			}
 
-			fp_comb << RemoveLegacyUserUniforms(pp_data.GetString()).GetChars();
+			fp_comb << RemoveLegacyUserUniforms(pp_data).GetChars();
 			fp_comb.Substitute("gl_TexCoord[0]", "vTexCoord");	// fix old custom shaders.
 
-			if (pp_data.GetString().IndexOf("ProcessLight") < 0)
+			if (pp_data.IndexOf("ProcessLight") < 0)
 			{
 				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().GetChars();
+				fp_comb << "\n" << pl_data.GetString();
 			}
 
 			// ProcessMaterial must be considered broken because it requires the user to fill in data they possibly cannot know all about.
-			if (pp_data.GetString().IndexOf("ProcessMaterial") >= 0 && pp_data.GetString().IndexOf("SetupMaterial") < 0)
+			if (pp_data.IndexOf("ProcessMaterial") >= 0 && pp_data.IndexOf("SetupMaterial") < 0)
 			{
 				// This reactivates the old logic and disables all features that cannot be supported with that method.
 				placeholder << "#define LEGACY_USER_SHADER\n";
@@ -491,7 +491,7 @@ 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().GetChars() << "\n";
+		fp_comb << pp_data.GetString() << "\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 2b6df32545..69729a8c7a 100644
--- a/src/common/rendering/gl/gl_shaderprogram.cpp
+++ b/src/common/rendering/gl/gl_shaderprogram.cpp
@@ -88,7 +88,7 @@ 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().GetChars();
+	FString code = fileSystem.ReadFile(lump).GetString();
 	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 61c1a720e9..16ff0eb65c 100644
--- a/src/common/rendering/gles/gles_shader.cpp
+++ b/src/common/rendering/gles/gles_shader.cpp
@@ -422,27 +422,27 @@ 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());
-			FileData pp_data = fileSystem.ReadFile(pp_lump);
+			FString pp_data = fileSystem.ReadFile(pp_lump).GetString();
 
-			if (pp_data.GetString().IndexOf("ProcessMaterial") < 0 && pp_data.GetString().IndexOf("SetupMaterial") < 0)
+			if (pp_data.IndexOf("ProcessMaterial") < 0 && pp_data.IndexOf("SetupMaterial") < 0)
 			{
 				// this looks like an old custom hardware shader.
 
-				if (pp_data.GetString().IndexOf("GetTexCoord") >= 0)
+				if (pp_data.IndexOf("GetTexCoord") >= 0)
 				{
 					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().GetChars();
+					fp_comb << "\n" << pl_data.GetString();
 				}
 				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().GetChars();
+					fp_comb << "\n" << pl_data.GetString();
 
-					if (pp_data.GetString().IndexOf("ProcessTexel") < 0)
+					if (pp_data.IndexOf("ProcessTexel") < 0)
 					{
 						// this looks like an even older custom hardware shader.
 						// We need to replace the ProcessTexel call to make it work.
@@ -451,7 +451,7 @@ bool FShader::Load(const char * name, const char * vert_prog_lump_, const char *
 					}
 				}
 
-				if (pp_data.GetString().IndexOf("ProcessLight") >= 0)
+				if (pp_data.IndexOf("ProcessLight") >= 0)
 				{
 					// The ProcessLight signatured changed. Forward to the old one.
 					fp_comb << "\nvec4 ProcessLight(vec4 color);\n";
@@ -459,19 +459,19 @@ bool FShader::Load(const char * name, const char * vert_prog_lump_, const char *
 				}
 			}
 
-			fp_comb << RemoveLegacyUserUniforms(pp_data.GetString()).GetChars();
+			fp_comb << RemoveLegacyUserUniforms(pp_data).GetChars();
 			fp_comb.Substitute("gl_TexCoord[0]", "vTexCoord");	// fix old custom shaders.
 
-			if (pp_data.GetString().IndexOf("ProcessLight") < 0)
+			if (pp_data.IndexOf("ProcessLight") < 0)
 			{
 				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().GetChars();
+				fp_comb << "\n" << pl_data.GetString();
 			}
 
 			// ProcessMaterial must be considered broken because it requires the user to fill in data they possibly cannot know all about.
-			if (pp_data.GetString().IndexOf("ProcessMaterial") >= 0 && pp_data.GetString().IndexOf("SetupMaterial") < 0)
+			if (pp_data.IndexOf("ProcessMaterial") >= 0 && pp_data.IndexOf("SetupMaterial") < 0)
 			{
 				// This reactivates the old logic and disables all features that cannot be supported with that method.
 				placeholder << "#define LEGACY_USER_SHADER\n";
@@ -490,7 +490,7 @@ 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().GetChars() << "\n";
+		fp_comb << pp_data.GetString() << "\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 16bd1ebe96..8677257f33 100644
--- a/src/common/rendering/gles/gles_shaderprogram.cpp
+++ b/src/common/rendering/gles/gles_shaderprogram.cpp
@@ -88,7 +88,7 @@ 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().GetChars();
+	FString code = fileSystem.ReadFile(lump).GetString();
 	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 287762f77e..f83b01c938 100644
--- a/src/common/rendering/vulkan/shaders/vk_ppshader.cpp
+++ b/src/common/rendering/vulkan/shaders/vk_ppshader.cpp
@@ -66,7 +66,7 @@ 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().GetChars();
+	FString code = fileSystem.ReadFile(lump).GetString();
 
 	FString patchedCode;
 	patchedCode.AppendFormat("#version %d\n", 450);
diff --git a/src/common/scripting/interface/vmnatives.cpp b/src/common/scripting/interface/vmnatives.cpp
index f04e39d45f..4dcd568e48 100644
--- a/src/common/scripting/interface/vmnatives.cpp
+++ b/src/common/scripting/interface/vmnatives.cpp
@@ -843,7 +843,7 @@ 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() : FString());
+	ACTION_RETURN_STRING(isLumpValid ? fileSystem.ReadFile(lump).GetString() : "");
 }
 
 //==========================================================================