diff --git a/renderdoc/driver/gl/gl_renderstate.cpp b/renderdoc/driver/gl/gl_renderstate.cpp
index e046d8acd..c655047ec 100644
--- a/renderdoc/driver/gl/gl_renderstate.cpp
+++ b/renderdoc/driver/gl/gl_renderstate.cpp
@@ -83,7 +83,43 @@ bool PixelUnpackState::FastPath(GLsizei width, GLsizei height, GLsizei depth, GL
 	if(height > 0 && imageheight > 0 && height < imageheight)
 		return false;
 
-	if(dataformat != eGL_NONE && alignment > (int32_t)GetByteSize(1, 1, 1, dataformat, basetype))
+	if(alignment > (int32_t)GetByteSize(1, 1, 1, dataformat, basetype))
+		return false;
+
+	return true;
+}
+
+bool PixelUnpackState::FastPathCompressed(GLsizei width, GLsizei height, GLsizei depth)
+{
+	// compressedBlockSize and compressedBlockWidth must be set for any of the unpack params to be used
+	// if they are 0, all of the unpack params are ignored, so we go through the fast path (no unpacking)
+	if(compressedBlockSize == 0 || compressedBlockWidth == 0)
+		return true;
+
+	if(skipPixels)
+		return false;
+
+	if(width > 0 && rowlength > 0 && width < rowlength)
+		return false;
+
+	// the below two unpack params require compressedBlockHeight to be set so if we haven't "failed" to
+	// hit the fast path, none of the other params make a difference as they're ignored and we go through
+	// the fast path (no unpacking)
+	if(compressedBlockHeight == 0)
+		return true;
+
+	if(height > 0 && skipRows)
+		return false;
+
+	if(height > 0 && imageheight > 0 && height < imageheight)
+		return false;
+
+	// the final unpack param requires compressedBlockDepth to be set, as above if it's 0 then we can
+	// just go straight through the fast path (no unpacking)
+	if(compressedBlockDepth == 0)
+		return true;
+
+	if(depth > 0 && skipImages)
 		return false;
 
 	return true;
diff --git a/renderdoc/driver/gl/gl_renderstate.h b/renderdoc/driver/gl/gl_renderstate.h
index abc473885..d8448bd9d 100644
--- a/renderdoc/driver/gl/gl_renderstate.h
+++ b/renderdoc/driver/gl/gl_renderstate.h
@@ -44,7 +44,9 @@ struct PixelUnpackState
 	void Fetch(const GLHookSet *funcs, bool compressed);
 	void Apply(const GLHookSet *funcs, bool compressed);
 
-	bool FastPath(GLsizei width, GLsizei height, GLsizei depth, GLenum dataformat=eGL_NONE, GLenum basetype=eGL_NONE);
+	bool FastPath(GLsizei width, GLsizei height, GLsizei depth, GLenum dataformat, GLenum basetype);
+	bool FastPathCompressed(GLsizei width, GLsizei height, GLsizei depth);
+
 	byte *Unpack(byte *pixels, GLsizei width, GLsizei height, GLsizei depth, GLenum dataformat, GLenum basetype);
 	byte *UnpackCompressed(byte *pixels, GLsizei width, GLsizei height, GLsizei depth, GLsizei &imageSize);
 };
diff --git a/renderdoc/driver/gl/wrappers/gl_texture_funcs.cpp b/renderdoc/driver/gl/wrappers/gl_texture_funcs.cpp
index 77f13042a..5009297d0 100644
--- a/renderdoc/driver/gl/wrappers/gl_texture_funcs.cpp
+++ b/renderdoc/driver/gl/wrappers/gl_texture_funcs.cpp
@@ -2039,7 +2039,7 @@ bool WrappedOpenGL::Serialise_glCompressedTextureImage1DEXT(GLuint texture, GLen
 	{
 		PixelUnpackState unpack; unpack.Fetch(&m_Real, true);
 
-		if(unpack.FastPath(Width, 0, 0))
+		if(unpack.FastPathCompressed(Width, 0, 0))
 			srcPixels = (byte *)pixels;
 		else
 			srcPixels = unpackedPixels = unpack.UnpackCompressed((byte *)pixels, Width, 0, 0, imageSize);
@@ -2199,7 +2199,7 @@ bool WrappedOpenGL::Serialise_glCompressedTextureImage2DEXT(GLuint texture, GLen
 	{
 		PixelUnpackState unpack; unpack.Fetch(&m_Real, true);
 
-		if(unpack.FastPath(Width, Height, 0))
+		if(unpack.FastPathCompressed(Width, Height, 0))
 			srcPixels = (byte *)pixels;
 		else
 			srcPixels = unpackedPixels = unpack.UnpackCompressed((byte *)pixels, Width, Height, 0, imageSize);
@@ -2383,7 +2383,7 @@ bool WrappedOpenGL::Serialise_glCompressedTextureImage3DEXT(GLuint texture, GLen
 	{
 		PixelUnpackState unpack; unpack.Fetch(&m_Real, true);
 
-		if(unpack.FastPath(Width, Height, Depth))
+		if(unpack.FastPathCompressed(Width, Height, Depth))
 			srcPixels = (byte *)pixels;
 		else
 			srcPixels = unpackedPixels = unpack.UnpackCompressed((byte *)pixels, Width, Height, Depth, imageSize);
@@ -3689,7 +3689,7 @@ bool WrappedOpenGL::Serialise_glCompressedTextureSubImage1DEXT(GLuint texture, G
 	{
 		PixelUnpackState unpack; unpack.Fetch(&m_Real, true);
 
-		if(unpack.FastPath(Width, 0, 0))
+		if(unpack.FastPathCompressed(Width, 0, 0))
 			srcPixels = (byte *)pixels;
 		else
 			srcPixels = unpackedPixels = unpack.UnpackCompressed((byte *)pixels, Width, 0, 0, imageSize);
@@ -3817,7 +3817,7 @@ bool WrappedOpenGL::Serialise_glCompressedTextureSubImage2DEXT(GLuint texture, G
 	{
 		PixelUnpackState unpack; unpack.Fetch(&m_Real, true);
 
-		if(unpack.FastPath(Width, Height, 0))
+		if(unpack.FastPathCompressed(Width, Height, 0))
 			srcPixels = (byte *)pixels;
 		else
 			srcPixels = unpackedPixels = unpack.UnpackCompressed((byte *)pixels, Width, Height, 0, imageSize);
@@ -3947,7 +3947,7 @@ bool WrappedOpenGL::Serialise_glCompressedTextureSubImage3DEXT(GLuint texture, G
 	{
 		PixelUnpackState unpack; unpack.Fetch(&m_Real, true);
 
-		if(unpack.FastPath(Width, Height, Depth))
+		if(unpack.FastPathCompressed(Width, Height, Depth))
 			srcPixels = (byte *)pixels;
 		else
 			srcPixels = unpackedPixels = unpack.UnpackCompressed((byte *)pixels, Width, Height, Depth, imageSize);