diff --git a/rpn.c b/rpn.c
--- a/rpn.c
+++ b/rpn.c
@@ -50,6 +50,9 @@ int main(void)
 			push(x);
 			push(y);
 			break;
+		case 'd':
+			pop();
+			break;
 		default:
 			fprintf(stderr, "Unknown '%c'\n", sym);
 			return 1;