diff --git a/libgfortran/ChangeLog b/libgfortran/ChangeLog
index 876b2c92f8a..29efe0ad486 100644
--- a/libgfortran/ChangeLog
+++ b/libgfortran/ChangeLog
@@ -1,3 +1,9 @@
+2015-07-29  Uros Bizjak  <ubizjak@gmail.com>
+
+	PR libgfortran/66650
+	* libgfortran.h (GFC_DTYPE_SIZE_MASK): Rewrite to avoid
+	"left shift of negative value" warning.
+
 2015-07-14  Janne Blomqvist  <jb@gcc.gnu.org>
 
 	PR libfortran/66861
diff --git a/libgfortran/libgfortran.h b/libgfortran/libgfortran.h
index 8962154aae7..39e5e4ae642 100644
--- a/libgfortran/libgfortran.h
+++ b/libgfortran/libgfortran.h
@@ -404,8 +404,7 @@ typedef GFC_ARRAY_DESCRIPTOR (GFC_MAX_DIMENSIONS, GFC_LOGICAL_16) gfc_array_l16;
 
 /* Macros to get both the size and the type with a single masking operation  */
 
-#define GFC_DTYPE_SIZE_MASK \
-  ((~((index_type) 0) >> GFC_DTYPE_SIZE_SHIFT) << GFC_DTYPE_SIZE_SHIFT)
+#define GFC_DTYPE_SIZE_MASK (-((index_type) 1 << GFC_DTYPE_SIZE_SHIFT))
 #define GFC_DTYPE_TYPE_SIZE_MASK (GFC_DTYPE_SIZE_MASK | GFC_DTYPE_TYPE_MASK)
 
 #define GFC_DTYPE_TYPE_SIZE(desc) ((desc)->dtype & GFC_DTYPE_TYPE_SIZE_MASK)