diff --git a/src/gl/api/gl_api.h b/src/gl/api/gl_api.h
index bcb03c416..3ed1a2efd 100644
--- a/src/gl/api/gl_api.h
+++ b/src/gl/api/gl_api.h
@@ -1,7 +1,7 @@
-#if defined(__APPLE__)
+#if defined(__unix__) || defined(__APPLE__)
 #define APIENTRY
 #define APIENTRYP *
-#endif // __APPLE__
+#endif // __unix__ || __APPLE__
 
 #ifndef __EXTERN
 #define __EXTERN extern
diff --git a/src/gl/data/gl_data.cpp b/src/gl/data/gl_data.cpp
index 20ec8a3a7..e0bb5ee6b 100644
--- a/src/gl/data/gl_data.cpp
+++ b/src/gl/data/gl_data.cpp
@@ -110,6 +110,7 @@ void AdjustSpriteOffsets()
 		FScanner sc;
 		sc.OpenLumpNum(lump);
 		GLRenderer->FlushTextures();
+		int ofslumpno = Wads.GetLumpFile(lump);
 		while (sc.GetString())
 		{
 			int x,y;
@@ -124,11 +125,11 @@ void AdjustSpriteOffsets()
 				FTexture * tex = TexMan[texno];
 
 				int lumpnum = tex->GetSourceLump();
-				// We only want to change texture offsets for sprites in the IWAD!
+				// We only want to change texture offsets for sprites in the IWAD or the file this lump originated from.
 				if (lumpnum >= 0 && lumpnum < Wads.GetNumLumps())
 				{
 					int wadno = Wads.GetLumpFile(lumpnum);
-					if (wadno==FWadCollection::IWAD_FILENUM)
+					if (wadno==FWadCollection::IWAD_FILENUM || wadno == ofslumpno)
 					{
 						tex->LeftOffset=x;
 						tex->TopOffset=y;
diff --git a/src/gl/system/gl_system.h b/src/gl/system/gl_system.h
index 8a0c307fc..222fb44f1 100644
--- a/src/gl/system/gl_system.h
+++ b/src/gl/system/gl_system.h
@@ -66,14 +66,18 @@
 #include <sys/stat.h>
 #include <fcntl.h>
 
+//GL headers
 #if defined(__APPLE__)
 #include <GL/glew.h>
 #include <OpenGL/OpenGL.h>
-#else // !__APPLE__
+#elif defined(__unix__)
+#include <GL/glew.h>
+#include "gl/api/glext.h"
+#else // !__APPLE__ && !__unix__
 #include <GL/gl.h>
 #include <GL/glu.h>
-#include "gl/api/glext.h"	//  use the local copy
-#endif // __APPLE__
+#include "gl/api/glext.h"
+#endif
 #include "gl/api/gl_api.h"
 
 #ifdef _WIN32