diff --git a/tests/test_texture_formats.h b/tests/test_texture_formats.h
index 172e0c9..0e9c0e0 100644
--- a/tests/test_texture_formats.h
+++ b/tests/test_texture_formats.h
@@ -188,6 +188,11 @@ public:
     /* ------------------------------------------------- glTexSubImage2D */
 
     void test_subimage_updates_only_target_region() {
+        /* The 2-wide RGB sub-image below is tightly packed (6 bytes/row), so it
+         * does not satisfy the default GL_UNPACK_ALIGNMENT of 4 (which would pad
+         * each row to 8 bytes). Tell GL the rows are tightly packed. */
+        glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
+
         /* Start with an all-black 16x16 RGB565 texture. */
         std::vector<uint8_t> img(16 * 16 * 3, 0);
         glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 16, 16, 0, GL_RGB, GL_UNSIGNED_BYTE, img.data());
diff --git a/tools/gl_test.h b/tools/gl_test.h
index 152fb4b..1ad3a6a 100644
--- a/tools/gl_test.h
+++ b/tools/gl_test.h
@@ -78,6 +78,10 @@ public:
         glDepthFunc(GL_LESS);
         glShadeModel(GL_SMOOTH);
 
+        /* Restore the spec default so a test that changes pixel-store state
+         * doesn't leak into the next (we no longer re-init per test). */
+        glPixelStorei(GL_UNPACK_ALIGNMENT, 4);
+
         glBindTexture(GL_TEXTURE_2D, 0);
 
         glMatrixMode(GL_PROJECTION); glLoadIdentity();