diff --git a/glx/singlesize.c b/glx/singlesize.c
index 4c60b6920..adbd32af8 100644
--- a/glx/singlesize.c
+++ b/glx/singlesize.c
@@ -107,7 +107,7 @@ __glGetMap_size(GLenum target, GLenum query)
         }
         break;
     }
-    return -1;
+    return 0;
 }
 
 GLint
@@ -166,7 +166,7 @@ __glGetPixelMap_size(GLenum map)
         query = GL_PIXEL_MAP_A_TO_A_SIZE;
         break;
     default:
-        return -1;
+        return 0;
     }
     glGetIntegerv(query, &size);
     return size;