diff --git a/src/gl/renderer/gl_renderstate.cpp b/src/gl/renderer/gl_renderstate.cpp
index 83303d61e7..56b319f008 100644
--- a/src/gl/renderer/gl_renderstate.cpp
+++ b/src/gl/renderer/gl_renderstate.cpp
@@ -80,19 +80,44 @@ void FRenderState::Reset()
 	mDstBlend = GL_ONE_MINUS_SRC_ALPHA;
 	mAlphaThreshold = 0.5f;
 	mBlendEquation = GL_FUNC_ADD;
+	mModelMatrixEnabled = false;
+	mTextureMatrixEnabled = false;
 	mObjectColor = 0xffffffff;
 	mVertexBuffer = mCurrentVertexBuffer = NULL;
 	mColormapState = CM_DEFAULT;
+	mSoftLight = 0;
+	mLightParms[0] = mLightParms[1] = mLightParms[2] = 0.0f;
 	mLightParms[3] = -1.f;
 	mSpecialEffect = EFF_NONE;
 	mClipHeight = 0.f;
 	mClipHeightDirection = 0.f;
+	mShaderTimer = 0.0f;
 	ClearClipSplit();
 
 	stSrcBlend = stDstBlend = -1;
 	stBlendEquation = -1;
 	stAlphaThreshold = -1.f;
+	stAlphaTest = 0;
 	mLastDepthClamp = true;
+	mInterpolationFactor = 0.0f;
+
+	mColor.Set(0.0f, 0.0f, 0.0f, 0.0f);
+	mCameraPos.Set(0.0f, 0.0f, 0.0f, 0.0f);
+	mGlowTop.Set(0.0f, 0.0f, 0.0f, 0.0f);
+	mGlowBottom.Set(0.0f, 0.0f, 0.0f, 0.0f);
+	mGlowTopPlane.Set(0.0f, 0.0f, 0.0f, 0.0f);
+	mGlowBottomPlane.Set(0.0f, 0.0f, 0.0f, 0.0f);
+	mSplitTopPlane.Set(0.0f, 0.0f, 0.0f, 0.0f);
+	mSplitBottomPlane.Set(0.0f, 0.0f, 0.0f, 0.0f);
+	mClipLine.Set(0.0f, 0.0f, 0.0f, 0.0f);
+	mDynColor.Set(0.0f, 0.0f, 0.0f, 0.0f);
+	mClipSplit[0] = mClipSplit[1] = 0.0f;
+	mEffectState = 0;
+	activeShader = nullptr;
+	mProjectionMatrix.loadIdentity();
+	mViewMatrix.loadIdentity();
+	mModelMatrix.loadIdentity();
+	mTextureMatrix.loadIdentity();
 }
 
 //==========================================================================
diff --git a/src/gl/system/gl_framebuffer.cpp b/src/gl/system/gl_framebuffer.cpp
index 6d56c1b27f..ec8b3f599e 100644
--- a/src/gl/system/gl_framebuffer.cpp
+++ b/src/gl/system/gl_framebuffer.cpp
@@ -99,6 +99,11 @@ OpenGLFrameBuffer::OpenGLFrameBuffer(void *hMonitor, int width, int height, int
 	// If wglSwapIntervalEXT is called after glBindFramebuffer in a frame the setting is not changed!
 	SetVSync(vid_vsync);
 
+	// Make sure all global variables tracking OpenGL context state are reset..
+	FHardwareTexture::InitGlobalState();
+	FMaterial::InitGlobalState();
+	gl_RenderState.Reset();
+
 	GLRenderer = new FGLRenderer(this);
 	memcpy (SourcePalette, GPalette.BaseColors, sizeof(PalEntry)*256);
 	UpdatePalette ();
diff --git a/src/gl/textures/gl_hwtexture.h b/src/gl/textures/gl_hwtexture.h
index 9b7028f8cd..4c00af272c 100644
--- a/src/gl/textures/gl_hwtexture.h
+++ b/src/gl/textures/gl_hwtexture.h
@@ -48,11 +48,11 @@ private:
 public:
 
 	static unsigned int lastbound[MAX_TEXTURES];
-	static int lastactivetexture;
-	static int max_texturesize;
 
 	static int GetTexDimension(int value);
 
+	static void InitGlobalState() { for (int i = 0; i < MAX_TEXTURES; i++) lastbound[i] = 0; }
+
 private:
 
 	short texwidth, texheight;
diff --git a/src/gl/textures/gl_material.cpp b/src/gl/textures/gl_material.cpp
index 8e0ab73e69..6ba1fe4b0c 100644
--- a/src/gl/textures/gl_material.cpp
+++ b/src/gl/textures/gl_material.cpp
@@ -669,6 +669,12 @@ static FMaterial *last;
 static int lastclamp;
 static int lasttrans;
 
+void FMaterial::InitGlobalState()
+{
+	last = nullptr;
+	lastclamp = 0;
+	lasttrans = 0;
+}
 
 void FMaterial::Bind(int clampmode, int translation)
 {
diff --git a/src/gl/textures/gl_material.h b/src/gl/textures/gl_material.h
index dea0d4cf57..d44a845f6f 100644
--- a/src/gl/textures/gl_material.h
+++ b/src/gl/textures/gl_material.h
@@ -263,6 +263,7 @@ public:
 	static FMaterial *ValidateTexture(FTextureID no, bool expand, bool trans);
 	static void ClearLastTexture();
 
+	static void InitGlobalState();
 };
 
 #endif