diff --git a/Makefile b/Makefile
index 7e832c6b..b857be6b 100644
--- a/Makefile
+++ b/Makefile
@@ -144,7 +144,7 @@ endif
 # Highest supported optimizations are -O2, higher levels
 # will likely break this crappy code.
 ifdef DEBUG
-CFLAGS ?= -O0 -g -Wall -pipe
+CFLAGS ?= -O0 -g -Wall -pipe -DDEBUG
 ifdef ASAN
 override CFLAGS += -fsanitize=address -DUSE_SANITIZER
 endif
diff --git a/src/client/refresh/gl1/gl1_image.c b/src/client/refresh/gl1/gl1_image.c
index 22b2e808..196667a4 100644
--- a/src/client/refresh/gl1/gl1_image.c
+++ b/src/client/refresh/gl1/gl1_image.c
@@ -559,11 +559,11 @@ R_Upload32Native(unsigned *data, int width, int height, qboolean mipmap)
 			break;
 		}
 	}
-    glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, mipmap);
+	glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, mipmap);
 	glTexImage2D(GL_TEXTURE_2D, 0, comp, width,
 			height, 0, GL_RGBA, GL_UNSIGNED_BYTE,
 			data);
-    glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, false);
+	glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, false);
 	return samples == gl_alpha_format;
 }
 
diff --git a/src/client/refresh/gl1/gl1_main.c b/src/client/refresh/gl1/gl1_main.c
index e0f3716e..73fc9e66 100644
--- a/src/client/refresh/gl1/gl1_main.c
+++ b/src/client/refresh/gl1/gl1_main.c
@@ -1405,6 +1405,10 @@ RI_Init(void)
 	R_Printf(PRINT_ALL, "Refresh: " REF_VERSION "\n");
 	R_Printf(PRINT_ALL, "Client: " YQ2VERSION "\n\n");
 
+#ifdef DEBUG
+	R_Printf(PRINT_ALL, "ref_gl1::R_Init() - DEBUG mode enabled\n");
+#endif
+
 	GetPCXPalette (&colormap, d_8to24table);
 	free(colormap);
 
@@ -1981,3 +1985,32 @@ Com_Printf(const char *msg, ...)
 	ri.Com_VPrintf(PRINT_ALL, msg, argptr);
 	va_end(argptr);
 }
+
+#ifdef DEBUG
+void
+glCheckError_(const char *file, const char *function, int line)
+{
+	GLenum errorCode;
+	const char * msg;
+
+#define MY_ERROR_CASE(X) case X : msg = #X; break;
+
+	while ((errorCode = glGetError()) != GL_NO_ERROR)
+	{
+		switch(errorCode)
+		{
+			MY_ERROR_CASE(GL_INVALID_ENUM);
+			MY_ERROR_CASE(GL_INVALID_VALUE);
+			MY_ERROR_CASE(GL_INVALID_OPERATION);
+			MY_ERROR_CASE(GL_STACK_OVERFLOW);
+			MY_ERROR_CASE(GL_STACK_UNDERFLOW);
+			MY_ERROR_CASE(GL_OUT_OF_MEMORY);
+			default: msg = "UNKNOWN";
+		}
+		R_Printf(PRINT_ALL, "glError: %s in %s (%s, %d)\n", msg, function, file, line);
+	}
+
+#undef MY_ERROR_CASE
+
+}
+#endif
diff --git a/src/client/refresh/gl1/header/local.h b/src/client/refresh/gl1/header/local.h
index ac60f428..5ca9d2a9 100644
--- a/src/client/refresh/gl1/header/local.h
+++ b/src/client/refresh/gl1/header/local.h
@@ -303,6 +303,55 @@ void R_TextureAlphaMode(char *string);
 void R_TextureSolidMode(char *string);
 int Scrap_AllocBlock(int w, int h, int *x, int *y);
 
+#ifdef DEBUG
+void glCheckError_(const char *file, const char *function, int line);
+// Ideally, the following list should contain all OpenGL calls.
+// Either way, errors are caught, since error flags are persisted until the next glGetError() call.
+// So they show, even if the location of the error is inaccurate.
+#define glDrawArrays(...) glDrawArrays(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glTexImage2D(...) glTexImage2D(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glTexSubImage2D(...) glTexSubImage2D(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glTexEnvf(...) glTexEnvf(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glTexEnvi(...) glTexEnvi(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glVertexPointer(...) glVertexPointer(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glTexCoordPointer(...) glTexCoordPointer(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glColorPointer(...) glColorPointer(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glTexParameteri(...) glTexParameteri(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glBindTexture(...) glBindTexture(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glFrustum(...) glFrustum(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glTranslatef(...) glTranslatef(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glRotatef(...) glRotatef(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glScalef(...) glScalef(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glScissor(...) glScissor(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glBlendFunc(...) glBlendFunc(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glDepthFunc(...) glDepthFunc(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glDepthMask(...) glDepthMask(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glDepthRange(...) glDepthRange(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glEnable(...) glEnable(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glDisable(...) glDisable(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glEnableClientState(...) glEnableClientState(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glDisableClientState(...) glDisableClientState(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glPushMatrix(...) glPushMatrix(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glPopMatrix(...) glPopMatrix(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glMatrixMode(...) glMatrixMode(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glOrtho(...) glOrtho(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glColorMask(...) glColorMask(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glStencilOp(...) glStencilOp(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glStencilFunc(...) glStencilFunc(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glDrawBuffer(...) glDrawBuffer(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glReadPixels(...) glReadPixels(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glClear(...) glClear(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glClearColor(...) glClearColor(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glClearStencil(...) glClearStencil(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glDeleteTextures(...) glDeleteTextures(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glFinish() glFinish(); glCheckError_(__FILE__, __func__, __LINE__)
+#define glAlphaFunc(...) glAlphaFunc(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glHint(...) glHint(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glLoadIdentity() glLoadIdentity(); glCheckError_(__FILE__, __func__, __LINE__)
+#define glBegin(...) glBegin(__VA_ARGS__); glCheckError_(__FILE__, __func__, __LINE__)
+#define glEnd() glEnd(); glCheckError_(__FILE__, __func__, __LINE__)
+#endif
+
 /* GL extension emulation functions */
 void R_DrawParticles2(int n,
 		const particle_t particles[],