diff --git a/cogl/driver/gl/cogl-texture-driver-gl.c b/cogl/driver/gl/cogl-texture-driver-gl.c
index 6cb004844..3c2296e69 100644
--- a/cogl/driver/gl/cogl-texture-driver-gl.c
+++ b/cogl/driver/gl/cogl-texture-driver-gl.c
@@ -400,7 +400,7 @@ _cogl_texture_driver_pixel_format_to_gl (CoglPixelFormat  format,
 {
   CoglPixelFormat required_format;
   GLenum glintformat;
-  GLenum glformat;
+  GLenum glformat = 0;
   GLenum gltype;
 
   required_format = format;
@@ -522,6 +522,10 @@ _cogl_texture_driver_pixel_format_to_gl (CoglPixelFormat  format,
       break;
     }
 
+  /* All of the pixel formats are handled above so if this hits then
+     we've been given an invalid pixel format */
+  g_assert (glformat != 0);
+
   if (out_glintformat != NULL)
     *out_glintformat = glintformat;
   if (out_glformat != NULL)
diff --git a/cogl/driver/gles/cogl-texture-driver-gles.c b/cogl/driver/gles/cogl-texture-driver-gles.c
index 3c83a4558..817ee93f9 100644
--- a/cogl/driver/gles/cogl-texture-driver-gles.c
+++ b/cogl/driver/gles/cogl-texture-driver-gles.c
@@ -412,7 +412,7 @@ _cogl_texture_driver_pixel_format_to_gl (CoglPixelFormat  format,
 {
   CoglPixelFormat required_format;
   GLenum glintformat;
-  GLenum glformat;
+  GLenum glformat = 0;
   GLenum gltype;
 
   required_format = format;
@@ -491,6 +491,10 @@ _cogl_texture_driver_pixel_format_to_gl (CoglPixelFormat  format,
       break;
     }
 
+  /* All of the pixel formats are handled above so if this hits then
+     we've been given an invalid pixel format */
+  g_assert (glformat != 0);
+
   if (out_glintformat != NULL)
     *out_glintformat = glintformat;
   if (out_glformat != NULL)