diff --git a/mach/vc4/as/mach5.c b/mach/vc4/as/mach5.c
index 350806e11..e98f67594 100644
--- a/mach/vc4/as/mach5.c
+++ b/mach/vc4/as/mach5.c
@@ -174,13 +174,11 @@ void stack_instr(quad opcode, int loreg, int hireg, int extrareg)
         case 26: /* lr */
             extrareg = 26;
             hireg = loreg = -1;
-            b = 0;
             break;
 
 		case 31: /* pc */
 			extrareg = 31;
 			hireg = loreg = -1;
-			b = 0;
 			break;
 
 		default:
@@ -204,7 +202,10 @@ void stack_instr(quad opcode, int loreg, int hireg, int extrareg)
 		serror("invalid register range");
 
 	if (hireg == -1)
-		m = 31;
+	{
+		b = 3;
+		m = 15;
+	}
 	else
 		m = hireg - loreg;