diff --git a/test/headless.cpp b/test/headless.cpp
index 3837beb9a..0f4e10027 100644
--- a/test/headless.cpp
+++ b/test/headless.cpp
@@ -104,7 +104,7 @@ TEST_P(HeadlessTest, render) {
         const int stride = w * 4;
         auto tmp = std::unique_ptr<char[]>(new char[stride]());
         char *rgba = reinterpret_cast<char *>(pixels.get());
-        for (int i = 0, j = height - 2; i < j; i++, j--) {
+        for (int i = 0, j = height - 1; i < j; i++, j--) {
             memcpy(tmp.get(), rgba + i * stride, stride);
             memcpy(rgba + i * stride, rgba + j * stride, stride);
             memcpy(rgba + j * stride, tmp.get(), stride);