--- a/config/config.mk
+++ b/config/config.mk
@@ -426,20 +426,20 @@ HOST_CMMFLAGS += -fobjc-exceptions
 OS_COMPILE_CMFLAGS += -fobjc-exceptions
 OS_COMPILE_CMMFLAGS += -fobjc-exceptions
 ifeq ($(MOZ_WIDGET_TOOLKIT),uikit)
 OS_COMPILE_CMFLAGS += -fobjc-abi-version=2 -fobjc-legacy-dispatch
 OS_COMPILE_CMMFLAGS += -fobjc-abi-version=2 -fobjc-legacy-dispatch
 endif
 endif
 
-COMPILE_CFLAGS	= $(VISIBILITY_FLAGS) $(DEFINES) $(INCLUDES) $(OS_INCLUDES) $(DSO_CFLAGS) $(DSO_PIC_CFLAGS) $(RTL_FLAGS) $(OS_CPPFLAGS) $(OS_COMPILE_CFLAGS) $(CFLAGS) $(MOZBUILD_CFLAGS) $(EXTRA_COMPILE_FLAGS)
-COMPILE_CXXFLAGS = $(if $(DISABLE_STL_WRAPPING),,$(STL_FLAGS)) $(VISIBILITY_FLAGS) $(DEFINES) $(INCLUDES) $(OS_INCLUDES) $(DSO_CFLAGS) $(DSO_PIC_CFLAGS) $(RTL_FLAGS) $(OS_CPPFLAGS) $(OS_COMPILE_CXXFLAGS) $(CXXFLAGS) $(MOZBUILD_CXXFLAGS) $(EXTRA_COMPILE_FLAGS)
-COMPILE_CMFLAGS = $(OS_COMPILE_CMFLAGS) $(MOZBUILD_CMFLAGS) $(EXTRA_COMPILE_FLAGS)
-COMPILE_CMMFLAGS = $(OS_COMPILE_CMMFLAGS) $(MOZBUILD_CMMFLAGS) $(EXTRA_COMPILE_FLAGS)
+COMPILE_CFLAGS	= $(VISIBILITY_FLAGS) $(DEFINES) $(INCLUDES) $(OS_INCLUDES) $(DSO_CFLAGS) $(DSO_PIC_CFLAGS) $(RTL_FLAGS) $(OS_CPPFLAGS) $(OS_COMPILE_CFLAGS) $(CFLAGS) $(MOZBUILD_CFLAGS)
+COMPILE_CXXFLAGS = $(if $(DISABLE_STL_WRAPPING),,$(STL_FLAGS)) $(VISIBILITY_FLAGS) $(DEFINES) $(INCLUDES) $(OS_INCLUDES) $(DSO_CFLAGS) $(DSO_PIC_CFLAGS) $(RTL_FLAGS) $(OS_CPPFLAGS) $(OS_COMPILE_CXXFLAGS) $(CXXFLAGS) $(MOZBUILD_CXXFLAGS)
+COMPILE_CMFLAGS = $(OS_COMPILE_CMFLAGS) $(MOZBUILD_CMFLAGS)
+COMPILE_CMMFLAGS = $(OS_COMPILE_CMMFLAGS) $(MOZBUILD_CMMFLAGS)
 ASFLAGS += $(MOZBUILD_ASFLAGS) $(EXTRA_ASSEMBLER_FLAGS)
 
 ifndef CROSS_COMPILE
 HOST_CFLAGS += $(RTL_FLAGS)
 endif
 
 #
 # Name of the binary code directories

--- a/python/mozbuild/mozbuild/frontend/emitter.py
+++ b/python/mozbuild/mozbuild/frontend/emitter.py
@@ -550,17 +550,16 @@ class TreeMetadataEmitter(LoggingMixin):
         # them. We should aim to keep this set small because it violates the
         # desired abstraction of the build definition away from makefiles.
         passthru = VariablePassthru(context)
         varlist = [
             'ANDROID_GENERATED_RESFILES',
             'ANDROID_RES_DIRS',
             'DISABLE_STL_WRAPPING',
             'EXTRA_ASSEMBLER_FLAGS',
-            'EXTRA_COMPILE_FLAGS',
             'EXTRA_COMPONENTS',
             'EXTRA_DSO_LDOPTS',
             'EXTRA_PP_COMPONENTS',
             'FAIL_ON_WARNINGS',
             'USE_STATIC_LIBS',
             'NO_DIST_INSTALL',
             'PYTHON_UNIT_TESTS',
             'RCFILE',

--- a/python/mozbuild/mozbuild/frontend/gyp_reader.py
+++ b/python/mozbuild/mozbuild/frontend/gyp_reader.py
@@ -2,16 +2,17 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 from __future__ import unicode_literals
 import gyp
 import sys
 import time
 import os
+from itertools import chain
 import mozpack.path as mozpath
 from mozpack.files import FileFinder
 from .sandbox import alphabetical_sorted
 from .context import (
     TemplateContext,
     VARIABLES,
 )
 from mozbuild.util import (
@@ -67,17 +68,16 @@ class GypContext(TemplateContext):
     @classmethod
     @memoize
     def VARIABLES(cls):
         """Returns the allowed variables for a GypContext."""
         # Using a class method instead of a class variable to hide the content
         # from sphinx.
         return dict(VARIABLES,
         EXTRA_ASSEMBLER_FLAGS=(List, list, '', None),
-        EXTRA_COMPILE_FLAGS=(List, list, '', None),
     )
 
 
 def encode(value):
     if isinstance(value, unicode):
         return value.encode('utf-8')
     return value
 
@@ -199,17 +199,35 @@ def read_from_gyp(config, path, output, 
                     resolved = mozpath.abspath(mozpath.join(config.topsrcdir, include[1:]))
                 else:
                     resolved = mozpath.abspath(mozpath.join(mozpath.dirname(build_file), include))
                 if not os.path.exists(resolved):
                     continue
                 context['LOCAL_INCLUDES'] += [include]
 
             context['EXTRA_ASSEMBLER_FLAGS'] = target_conf.get('asflags_mozilla', [])
-            context['EXTRA_COMPILE_FLAGS'] = target_conf.get('cflags_mozilla', [])
+            flags = target_conf.get('cflags_mozilla', [])
+            if flags:
+                suffix_map = {
+                    '.c': 'CFLAGS',
+                    '.cpp': 'CXXFLAGS',
+                    '.cc': 'CXXFLAGS',
+                    '.m': 'CMFLAGS',
+                    '.mm': 'CMMFLAGS',
+                }
+                extensions = {
+                    mozpath.splitext(f)[-1]
+                    for f in chain(sources, unified_sources)
+                }
+                variables = (
+                    suffix_map[e]
+                    for e in extensions if e in suffix_map
+                )
+                for var in variables:
+                    context[var].extend(flags)
         else:
             # Ignore other types than static_library because we don't have
             # anything using them, and we're not testing them. They can be
             # added when that becomes necessary.
             raise NotImplementedError('Unsupported gyp target type: %s' % spec['type'])
 
         # Add some features to all contexts. Put here in case LOCAL_INCLUDES
         # order matters.