diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index ded59707617..41dcb5d6ca5 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2016-11-28  Markus Trippelsdorf  <markus@trippelsdorf.de>
+
+	PR target/78556
+	* config/rs6000/rs6000.c (vspltis_constant): Add casts to avoid
+	left shifting of negative values.
+
 2016-11-28  Jakub Jelinek  <jakub@redhat.com>
 
 	PR fortran/78298
diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index 6c28e6aaf65..dfb5dc86b11 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -6214,7 +6214,9 @@ vspltis_constant (rtx op, unsigned step, unsigned copies)
       bitsize /= 2;
       small_val = splat_val >> bitsize;
       mask >>= bitsize;
-      if (splat_val != ((small_val << bitsize) | (small_val & mask)))
+      if (splat_val != ((HOST_WIDE_INT)
+          ((unsigned HOST_WIDE_INT) small_val << bitsize)
+          | (small_val & mask)))
 	return false;
       splat_val = small_val;
     }