diff --git a/lib/src/gpu/uhdr_gl_utils.cpp b/lib/src/gpu/uhdr_gl_utils.cpp
index af86447f..50a248af 100644
--- a/lib/src/gpu/uhdr_gl_utils.cpp
+++ b/lib/src/gpu/uhdr_gl_utils.cpp
@@ -67,6 +67,11 @@ void uhdr_opengl_ctxt::init_opengl_ctxt() {
               "eglMakeCurrent() failed")
 #undef RET_IF_TRUE
 
+  // Image buffers handed to and read from this context are tightly packed (rows are w * bpp
+  // bytes), so texture uploads and read backs must not assume the default 4-byte row alignment.
+  glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
+  glPixelStorei(GL_PACK_ALIGNMENT, 1);
+
   setup_quad();
 }
 
@@ -184,9 +189,7 @@ GLuint uhdr_opengl_ctxt::create_texture(uhdr_img_fmt_t fmt, int w, int h, void*
       glTexImage2D(GL_TEXTURE_2D, 0, GL_R8, w, h * 3 / 2, 0, GL_RED, GL_UNSIGNED_BYTE, data);
       break;
     case UHDR_IMG_FMT_8bppYCbCr400:
-      glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
       glTexImage2D(GL_TEXTURE_2D, 0, GL_R8, w, h, 0, GL_RED, GL_UNSIGNED_BYTE, data);
-      glPixelStorei(GL_UNPACK_ALIGNMENT, 4);
       break;
     case UHDR_IMG_FMT_32bppRGBA8888:
       glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, w, h, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
@@ -343,9 +346,7 @@ void uhdr_opengl_ctxt::read_texture(GLuint* texture, uhdr_img_fmt_t fmt, int w,
   } else if (fmt == UHDR_IMG_FMT_64bppRGBAHalfFloat) {
     glReadPixels(0, 0, w, h, GL_RGBA, GL_HALF_FLOAT, data);
   } else if (fmt == UHDR_IMG_FMT_8bppYCbCr400) {
-    glPixelStorei(GL_PACK_ALIGNMENT, 1);
     glReadPixels(0, 0, w, h, GL_RED, GL_UNSIGNED_BYTE, data);
-    glPixelStorei(GL_PACK_ALIGNMENT, 4);
   }
   glBindFramebuffer(GL_FRAMEBUFFER, 0);
   glDeleteFramebuffers(1, &frm_buffer);
diff --git a/tests/editorhelper_test.cpp b/tests/editorhelper_test.cpp
index 975b543a..b20748c5 100644
--- a/tests/editorhelper_test.cpp
+++ b/tests/editorhelper_test.cpp
@@ -498,4 +498,48 @@ INSTANTIATE_TEST_SUITE_P(
                                          UHDR_IMG_FMT_64bppRGBAHalfFloat,
                                          UHDR_IMG_FMT_32bppRGBA8888)));
 
+#ifdef UHDR_ENABLE_GLES
+// Planes are tightly packed, so textures must hold exactly the bytes of the buffer for widths
+// whose rows are not a multiple of 4 bytes.
+TEST(OpenGLContextTest, TextureUploadOfTightlyPackedRows) {
+  uhdr_opengl_ctxt opengl_ctxt;
+  opengl_ctxt.init_opengl_ctxt();
+  if (opengl_ctxt.mErrorStatus.error_code != UHDR_CODEC_OK) {
+    GTEST_SKIP() << "opengl context unavailable";
+  }
+  struct {
+    uhdr_img_fmt_t fmt;
+    int rows_per_line;  // texture rows per image row, in halves
+    int bpp;
+  } formats[] = {
+      {UHDR_IMG_FMT_8bppYCbCr400, 2, 1},  {UHDR_IMG_FMT_12bppYCbCr420, 3, 1},
+      {UHDR_IMG_FMT_16bppYCbCr422, 4, 1}, {UHDR_IMG_FMT_24bppYCbCr444, 6, 1},
+      {UHDR_IMG_FMT_24bppRGB888, 2, 3},
+  };
+  const int ht = 8;
+  for (const auto& f : formats) {
+    for (int wd = 1; wd <= 10; wd++) {
+      std::string msg = "format: " + std::to_string(f.fmt) + " width: " + std::to_string(wd);
+      const int tex_ht = ht * f.rows_per_line / 2;
+      std::vector<uint8_t> src(static_cast<size_t>(wd) * tex_ht * f.bpp);
+      for (size_t i = 0; i < src.size(); i++) src[i] = static_cast<uint8_t>(i * 7 + 1);
+      GLuint texture = opengl_ctxt.create_texture(f.fmt, wd, ht, src.data());
+      ASSERT_NE(texture, 0u) << msg;
+      std::vector<uint8_t> dst;
+      if (f.bpp == 1) {
+        dst.resize(src.size());
+        opengl_ctxt.read_texture(&texture, UHDR_IMG_FMT_8bppYCbCr400, wd, tex_ht, dst.data());
+      } else {
+        std::vector<uint8_t> rgba(static_cast<size_t>(wd) * tex_ht * 4);
+        opengl_ctxt.read_texture(&texture, UHDR_IMG_FMT_32bppRGBA8888, wd, tex_ht, rgba.data());
+        for (size_t i = 0; i < rgba.size(); i += 4) dst.insert(dst.end(), &rgba[i], &rgba[i + 3]);
+      }
+      glDeleteTextures(1, &texture);
+      ASSERT_EQ(opengl_ctxt.mErrorStatus.error_code, UHDR_CODEC_OK) << msg;
+      ASSERT_EQ(src, dst) << msg;
+    }
+  }
+}
+#endif
+
 }  // namespace ultrahdr