diff --git a/drivers/char/drm/sis_mm.c b/drivers/char/drm/sis_mm.c
index 6be1c57..a6b7ccd 100644
--- a/drivers/char/drm/sis_mm.c
+++ b/drivers/char/drm/sis_mm.c
@@ -134,6 +134,7 @@
 		      dev_priv->agp_initialized)) {
 		DRM_ERROR
 		    ("Attempt to allocate from uninitialized memory manager.\n");
+		mutex_unlock(&dev->struct_mutex);
 		return -EINVAL;
 	}