diff --git a/lib/texpect/texpect.c b/lib/texpect/texpect.c
index 5657efa44d1..1a6ebf486ae 100644
--- a/lib/texpect/texpect.c
+++ b/lib/texpect/texpect.c
@@ -388,7 +388,13 @@ int main(int argc, const char **argv)
 	}
 
 	while ((optidx = poptGetNextOpt(pc)) != -1) {
-		;;
+		switch (optidx) {
+		case POPT_ERROR_BADOPT:
+			fprintf(stderr, "\nInvalid option %s: %s\n\n",
+				poptBadOption(pc, 0), poptStrerror(optidx));
+			poptPrintUsage(pc, stderr, 0);
+			exit(1);
+		}
 	}
 
 	instruction_file = poptGetArg(pc);