diff --git a/gtests/net/packetdrill/run_system_call.c b/gtests/net/packetdrill/run_system_call.c
index 28a94f463d81853dbb338adc9943edcccaad72ff..ae87a996849648930c9f3b968ed6e18e343691a5 100644
--- a/gtests/net/packetdrill/run_system_call.c
+++ b/gtests/net/packetdrill/run_system_call.c
@@ -663,7 +663,7 @@ int check_size_t_expr(struct expression *expr, size_t value, char *val_name, cha
 			return STATUS_ERR;
 		}
 		if (script_val != value) {
-			asprintf(error, "%s: expected: %u actual: %u", val_name, script_val, value);
+			asprintf(error, "%s: expected: %zu actual: %zu", val_name, script_val, value);
 			return STATUS_ERR;
 		}
 	}