Index: config/rs6000/rs6000.c
===================================================================
--- config/rs6000/rs6000.c	(revision 137784)
+++ config/rs6000/rs6000.c	(working copy)
@@ -12288,9 +12288,13 @@ print_operand (FILE *file, rtx x, int co
 	  fprintf (file, "0,%s", reg_names[REGNO (tmp)]);
 	else
 	  {
-	    gcc_assert (GET_CODE (tmp) == PLUS
-			&& REG_P (XEXP (tmp, 0))
-			&& REG_P (XEXP (tmp, 1)));
+	    if (!GET_CODE (tmp) == PLUS
+		|| !REG_P (XEXP (tmp, 0))
+		|| !REG_P (XEXP (tmp, 1)))
+	      {
+		output_operand_lossage ("invalid %%y value, try using the 'Z' constraint");
+		break;
+	      }
 
 	    if (REGNO (XEXP (tmp, 0)) == 0)
 	      fprintf (file, "%s,%s", reg_names[ REGNO (XEXP (tmp, 1)) ],
Index: testsuite/gcc.target/powerpc/asm-y.c
===================================================================
--- testsuite/gcc.target/powerpc/asm-y.c	(revision 0)
+++ testsuite/gcc.target/powerpc/asm-y.c	(revision 0)
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O1" } */
+
+/* Test that %yN does not cause an internal error if used incorrectly.  */
+
+int f(int *a)
+{
+  asm ("#%y0" : "=m"(a[2])); /* { dg-error "try using the 'Z' constraint" } */
+  asm ("#%y0" : "=m"(a[1])); /* { dg-error "try using the 'Z' constraint" } */
+  asm ("#%y0" : "=m"(a[0]));
+}