diff --git a/gfx/gl/moz.build b/gfx/gl/moz.build
index 52a6bf99f..38f753074 100644
--- a/gfx/gl/moz.build
+++ b/gfx/gl/moz.build
@@ -35,7 +35,6 @@ EXPORTS += [
     'GLContextEGL.h',
     'GLContextProvider.h',
     'GLContextProviderImpl.h',
-    'GLContextProviderX11.h',
     'GLContextSymbols.h',
     'GLContextTypes.h',
     'GLDefs.h',
@@ -58,8 +57,19 @@ EXPORTS += [
 if CONFIG['MOZ_X11']:
     EXPORTS += [
         'GLContextGLX.h',
+        'GLContextProviderX11.h',
         'GLXLibrary.h',
     ]
+    # GLContextProviderX11.cpp falls back to GLX, so keep the GLX provider
+    # available on all X11 builds even when EGL is the preferred provider.
+    # GLContextProviderGLX.cpp must stay out of UNIFIED_SOURCES because it
+    # includes X11 headers that cause conflicts there.
+    SOURCES += [
+        'GLContextProviderGLX.cpp',
+    ]
+    UNIFIED_SOURCES += [
+        'GLContextProviderX11.cpp',
+    ]
 
 # Win32 is a special snowflake, for ANGLE
 if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'windows':
@@ -108,11 +118,8 @@ elif gl_provider == 'EAGL':
         'GLContextEAGL.h',
     ]
 
-elif gl_provider == 'GLX':
-    # GLContextProviderGLX.cpp needs to be kept out of UNIFIED_SOURCES
-    # as it includes X11 headers which cause conflicts.
+if CONFIG['MOZ_X11'] and gl_provider == 'GLX':
     SOURCES += [
-        'GLContextProviderGLX.cpp',
         'SharedSurfaceGLX.cpp'
     ]
     EXPORTS += [
@@ -128,7 +135,6 @@ UNIFIED_SOURCES += [
     'GLContext.cpp',
     'GLContextFeatures.cpp',
     'GLContextProviderEGL.cpp',
-    'GLContextProviderX11.cpp',
     'GLContextTypes.cpp',
     'GLDebugUtils.cpp',
     'GLLibraryEGL.cpp',