--- a/js/src/gdb/moz.build
+++ b/js/src/gdb/moz.build
@@ -37,17 +37,17 @@ USE_LIBS += [
 if CONFIG['ENABLE_INTL_API'] and CONFIG['MOZ_ICU_DATA_ARCHIVE']:
     # The ICU libraries linked into libmozjs will not include the ICU data,
     # so link it directly.
     USE_LIBS += ['icudata']
 
 OS_LIBS += CONFIG['MOZ_ZLIB_LIBS']
 
 if CONFIG['GNU_CXX']:
-    CXXFLAGS += ['-Wno-shadow']
+    CXXFLAGS += ['-Wno-shadow', '-fno-strict-aliasing']
 
 # This is intended as a temporary workaround to enable VS2015.
 if CONFIG['_MSC_VER']:
     CXXFLAGS += ['-wd4312']
 
 DEFINES['topsrcdir'] = '%s/js/src' % TOPSRCDIR
 FINAL_TARGET_PP_FILES += ['gdb-tests-gdb.py.in']
 OBJDIR_FILES.js.src.gdb += ['!/dist/bin/gdb-tests-gdb.py']

--- a/js/src/jsapi-tests/moz.build
+++ b/js/src/jsapi-tests/moz.build
@@ -140,16 +140,16 @@ if CONFIG['ENABLE_INTL_API'] and CONFIG[
 
 USE_LIBS += [
     'static:js',
 ]
 
 OS_LIBS += CONFIG['MOZ_ZLIB_LIBS']
 
 if CONFIG['GNU_CXX']:
-    CXXFLAGS += ['-Wno-shadow', '-Werror=format']
+    CXXFLAGS += ['-Wno-shadow', '-Werror=format', '-fno-strict-aliasing']
 
 # This is intended as a temporary workaround to enable VS2015.
 if CONFIG['_MSC_VER']:
     CXXFLAGS += ['-wd4312']
 
 DEFINES['topsrcdir'] = '%s/js/src' % TOPSRCDIR
 OBJDIR_PP_FILES.js.src['jsapi-tests'] += ['jsapi-tests-gdb.py.in']