diff --git a/libgimpbase/gimpunit.c b/libgimpbase/gimpunit.c
index cbd4aa9fe4..aba477e954 100644
--- a/libgimpbase/gimpunit.c
+++ b/libgimpbase/gimpunit.c
@@ -109,7 +109,7 @@ string_to_unit (const GValue *src_value,
   return;
 
  error:
-  g_warning ("Can't convert string to GimpUnit.");
+  g_warning ("Can't convert string '%s' to GimpUnit.", str);
 }