diff --git a/opengl/libs/EGL/egl_display.cpp b/opengl/libs/EGL/egl_display.cpp
index 1ada33e..5b5afd3 100644
--- a/opengl/libs/EGL/egl_display.cpp
+++ b/opengl/libs/EGL/egl_display.cpp
@@ -254,6 +254,7 @@
         }
     }
 
+    std::vector<std::string> extensionStrings;
     { // scope for lock
         std::lock_guard<std::mutex> _l(lock);
 
@@ -315,16 +316,14 @@
         }
         mClientApiString = sClientApiString;
 
-        mExtensionString = gBuiltinExtensionString;
-
         // b/269060366 Conditionally enabled EGL_ANDROID_get_frame_timestamps extension if the
         // device's present timestamps are reliable (which may not be the case on emulators).
         if (cnx->angleLoaded) {
             if (android::base::GetBoolProperty("service.sf.present_timestamp", false)) {
-                mExtensionString.append("EGL_ANDROID_get_frame_timestamps ");
+                extensionStrings.push_back("EGL_ANDROID_get_frame_timestamps");
             }
         } else {
-            mExtensionString.append("EGL_ANDROID_get_frame_timestamps ");
+            extensionStrings.push_back("EGL_ANDROID_get_frame_timestamps");
         }
 
         hasColorSpaceSupport = findExtension(disp.queryString.extensions, "EGL_KHR_gl_colorspace");
@@ -335,10 +334,12 @@
 
         // Add wide-color extensions if device can support wide-color
         if (wideColorBoardConfig && hasColorSpaceSupport) {
-            mExtensionString.append(
-                    "EGL_EXT_gl_colorspace_scrgb EGL_EXT_gl_colorspace_scrgb_linear "
-                    "EGL_EXT_gl_colorspace_display_p3_linear EGL_EXT_gl_colorspace_display_p3 "
-                    "EGL_EXT_gl_colorspace_display_p3_passthrough ");
+            std::vector<std::string> wideColorExtensions =
+                    {"EGL_EXT_gl_colorspace_scrgb", "EGL_EXT_gl_colorspace_scrgb_linear",
+                     "EGL_EXT_gl_colorspace_display_p3_linear", "EGL_EXT_gl_colorspace_display_p3",
+                     "EGL_EXT_gl_colorspace_display_p3_passthrough"};
+            extensionStrings.insert(extensionStrings.end(), wideColorExtensions.begin(),
+                                    wideColorExtensions.end());
         }
 
         bool hasHdrBoardConfig = android::sysprop::has_HDR_display(false);
@@ -348,9 +349,11 @@
             // Typically that means there is an HDR capable display attached, but could be
             // support for attaching an HDR display. In either case, advertise support for
             // HDR color spaces.
-            mExtensionString.append("EGL_EXT_gl_colorspace_bt2020_hlg "
-                                    "EGL_EXT_gl_colorspace_bt2020_linear "
-                                    "EGL_EXT_gl_colorspace_bt2020_pq ");
+            std::vector<std::string> hdrExtensions = {"EGL_EXT_gl_colorspace_bt2020_hlg",
+                                                      "EGL_EXT_gl_colorspace_bt2020_linear",
+                                                      "EGL_EXT_gl_colorspace_bt2020_pq"};
+            extensionStrings.insert(extensionStrings.end(), hdrExtensions.begin(),
+                                    hdrExtensions.end());
         }
 
         char const* start = gExtensionString;
@@ -361,7 +364,7 @@
                 // NOTE: we could avoid the copy if we had strnstr.
                 const std::string ext(start, len);
                 if (findExtension(disp.queryString.extensions, ext.c_str(), len)) {
-                    mExtensionString.append(ext + " ");
+                    extensionStrings.push_back(ext);
                 }
                 // advance to the next extension name, skipping the space.
                 start += len;
@@ -388,6 +391,14 @@
         refCond.notify_all();
     }
 
+    auto mergeExtensionStrings = [](const std::vector<std::string>& strings) {
+        std::ostringstream combinedStringStream;
+        std::copy(strings.begin(), strings.end(),
+                  std::ostream_iterator<std::string>(combinedStringStream, " "));
+        // gBuiltinExtensionString already has a trailing space so is added here
+        return gBuiltinExtensionString + combinedStringStream.str();
+    };
+    mExtensionString = mergeExtensionStrings(extensionStrings);
     return EGL_TRUE;
 }
 
diff --git a/opengl/tests/EGLTest/Android.bp b/opengl/tests/EGLTest/Android.bp
index d96a895..aebd3f2 100644
--- a/opengl/tests/EGLTest/Android.bp
+++ b/opengl/tests/EGLTest/Android.bp
@@ -37,6 +37,11 @@
         "libSurfaceFlingerProp",
     ],
 
+    static_libs: [
+        "libgmock",
+        "libgtest",
+    ],
+
     include_dirs: [
         "frameworks/native/opengl/libs",
         "frameworks/native/opengl/libs/EGL",
diff --git a/opengl/tests/EGLTest/EGL_test.cpp b/opengl/tests/EGLTest/EGL_test.cpp
index cbe4ef9..503d7df 100644
--- a/opengl/tests/EGLTest/EGL_test.cpp
+++ b/opengl/tests/EGLTest/EGL_test.cpp
@@ -15,6 +15,7 @@
  */
 
 #include <gtest/gtest.h>
+#include <gmock/gmock.h>
 
 #include <SurfaceFlingerProperties.h>
 #include <android/hardware/configstore/1.0/ISurfaceFlingerConfigs.h>
@@ -29,6 +30,8 @@
 #include <gui/IGraphicBufferConsumer.h>
 #include <gui/BufferQueue.h>
 
+#include "egl_display.h"
+
 bool hasEglExtension(EGLDisplay dpy, const char* extensionName) {
     const char* exts = eglQueryString(dpy, EGL_EXTENSIONS);
     size_t cropExtLen = strlen(extensionName);
@@ -1011,4 +1014,57 @@
 
     EXPECT_TRUE(eglDestroySurface(mEglDisplay, eglSurface));
 }
+
+TEST_F(EGLTest, EGLCheckExtensionString) {
+    // check that the format of the extension string is correct
+
+    egl_display_t* display = egl_display_t::get(mEglDisplay);
+    ASSERT_NE(display, nullptr);
+
+    std::string extensionStrRegex = "((EGL_ANDROID_front_buffer_auto_refresh|"
+       "EGL_ANDROID_get_native_client_buffer|"
+       "EGL_ANDROID_presentation_time|"
+       "EGL_EXT_surface_CTA861_3_metadata|"
+       "EGL_EXT_surface_SMPTE2086_metadata|"
+       "EGL_KHR_get_all_proc_addresses|"
+       "EGL_KHR_swap_buffers_with_damage|"
+       "EGL_ANDROID_get_frame_timestamps|"
+       "EGL_EXT_gl_colorspace_scrgb|"
+       "EGL_EXT_gl_colorspace_scrgb_linear|"
+       "EGL_EXT_gl_colorspace_display_p3_linear|"
+       "EGL_EXT_gl_colorspace_display_p3|"
+       "EGL_EXT_gl_colorspace_display_p3_passthrough|"
+       "EGL_EXT_gl_colorspace_bt2020_hlg|"
+       "EGL_EXT_gl_colorspace_bt2020_linear|"
+       "EGL_EXT_gl_colorspace_bt2020_pq|"
+       "EGL_ANDROID_image_native_buffer|"
+       "EGL_ANDROID_native_fence_sync|"
+       "EGL_ANDROID_recordable|"
+       "EGL_EXT_create_context_robustness|"
+       "EGL_EXT_image_gl_colorspace|"
+       "EGL_EXT_pixel_format_float|"
+       "EGL_EXT_protected_content|"
+       "EGL_EXT_yuv_surface|"
+       "EGL_IMG_context_priority|"
+       "EGL_KHR_config_attribs|"
+       "EGL_KHR_create_context|"
+       "EGL_KHR_fence_sync|"
+       "EGL_KHR_gl_colorspace|"
+       "EGL_KHR_gl_renderbuffer_image|"
+       "EGL_KHR_gl_texture_2D_image|"
+       "EGL_KHR_gl_texture_3D_image|"
+       "EGL_KHR_gl_texture_cubemap_image|"
+       "EGL_KHR_image|"
+       "EGL_KHR_image_base|"
+       "EGL_KHR_mutable_render_buffer|"
+       "EGL_KHR_no_config_context|"
+       "EGL_KHR_partial_update|"
+       "EGL_KHR_surfaceless_context|"
+       "EGL_KHR_wait_sync|"
+       "EGL_EXT_buffer_age|"
+       "EGL_KHR_reusable_sync|"
+       "EGL_NV_context_priority_realtime) )+";
+    EXPECT_THAT(display->getExtensionString(), testing::MatchesRegex(extensionStrRegex));
+}
+
 }