diff --git a/assemble.c b/assemble.c
index 1b69dbb..6305545 100644
--- a/assemble.c
+++ b/assemble.c
@@ -1340,7 +1340,7 @@ static int assemble(
                                 return 0;
                             }
 
-                            if (op->value == 0100 && (mode.type & 070) == 0) {
+                            if (op->value == I_JMP && (mode.type & 070) == 0) {
                                 report(stack->top, "JMP Rn is illegal\n");
                                 /* But encode it anyway... */
                             }