diff --git a/python/mozbuild/mozbuild/frontend/emitter.py b/python/mozbuild/mozbuild/frontend/emitter.py
index cc2d1f3d827b..2924c770e24a 100644
--- a/python/mozbuild/mozbuild/frontend/emitter.py
+++ b/python/mozbuild/mozbuild/frontend/emitter.py
@@ -83,6 +83,7 @@ class TreeMetadataEmitter(object):
             ASFILES='ASFILES',
             CMMSRCS='CMMSRCS',
             CPPSRCS='CPP_SOURCES',
+            CPP_UNIT_TESTS='CPP_UNIT_TESTS',
             CSRCS='CSRCS',
             DEFINES='DEFINES',
             EXTRA_COMPONENTS='EXTRA_COMPONENTS',
diff --git a/python/mozbuild/mozbuild/frontend/sandbox_symbols.py b/python/mozbuild/mozbuild/frontend/sandbox_symbols.py
index 3160b76984a5..d9b4ac8b055c 100644
--- a/python/mozbuild/mozbuild/frontend/sandbox_symbols.py
+++ b/python/mozbuild/mozbuild/frontend/sandbox_symbols.py
@@ -119,6 +119,13 @@ VARIABLES = {
        files will be installed in the /components directory of the distribution.
         """),
 
+    'CPP_UNIT_TESTS': (StrictOrderingOnAppendList, list, [],
+        """C++ source files for unit tests.
+
+        This is a list of C++ unit test sources. Entries must be files that
+        exist. These generally have .cpp extensions.
+        """),
+
     'GTEST_C_SOURCES': (StrictOrderingOnAppendList, list, [],
         """C code source files for GTest unit tests.
 
diff --git a/python/mozbuild/mozbuild/test/backend/data/variable_passthru/moz.build b/python/mozbuild/mozbuild/test/backend/data/variable_passthru/moz.build
index 172be89b5d99..73a6c31f1c7a 100644
--- a/python/mozbuild/mozbuild/test/backend/data/variable_passthru/moz.build
+++ b/python/mozbuild/mozbuild/test/backend/data/variable_passthru/moz.build
@@ -13,6 +13,8 @@ DEFINES = ['-Dbar', '-Dfoo']
 EXTRA_COMPONENTS = ['bar.js', 'foo.js']
 EXTRA_PP_COMPONENTS = ['bar.pp.js', 'foo.pp.js']
 
+CPP_UNIT_TESTS = ['foo.cpp']
+
 GTEST_C_SOURCES = ['test1.c', 'test2.c']
 GTEST_CMM_SOURCES = ['test1.mm', 'test2.mm']
 GTEST_CPP_SOURCES = ['test1.cpp', 'test2.cpp']
diff --git a/python/mozbuild/mozbuild/test/backend/test_recursivemake.py b/python/mozbuild/mozbuild/test/backend/test_recursivemake.py
index f674aefe035e..95997ab96e30 100644
--- a/python/mozbuild/mozbuild/test/backend/test_recursivemake.py
+++ b/python/mozbuild/mozbuild/test/backend/test_recursivemake.py
@@ -147,6 +147,9 @@ class TestRecursiveMakeBackend(BackendTester):
                 'CMMSRCS += bar.mm',
                 'CMMSRCS += foo.mm',
             ],
+            'CPP_UNIT_TESTS': [
+                'CPP_UNIT_TESTS += foo.cpp',
+            ],
             'CSRCS': [
                 'CSRCS += bar.c',
                 'CSRCS += foo.c',
diff --git a/python/mozbuild/mozbuild/test/frontend/data/variable-passthru/moz.build b/python/mozbuild/mozbuild/test/frontend/data/variable-passthru/moz.build
index 60ad1bc8bb26..47813fd7f23e 100644
--- a/python/mozbuild/mozbuild/test/frontend/data/variable-passthru/moz.build
+++ b/python/mozbuild/mozbuild/test/frontend/data/variable-passthru/moz.build
@@ -13,6 +13,8 @@ DEFINES=['-Dfans', '-Dtans']
 EXTRA_COMPONENTS=['fans.js', 'tans.js']
 EXTRA_PP_COMPONENTS=['fans.pp.js', 'tans.pp.js']
 
+CPP_UNIT_TESTS = ['foo.cpp']
+
 GTEST_C_SOURCES = ['test1.c', 'test2.c']
 GTEST_CMM_SOURCES = ['test1.mm', 'test2.mm']
 GTEST_CPP_SOURCES = ['test1.cpp', 'test2.cpp']
diff --git a/python/mozbuild/mozbuild/test/frontend/test_emitter.py b/python/mozbuild/mozbuild/test/frontend/test_emitter.py
index d5134acf6172..baf1dd0b9646 100644
--- a/python/mozbuild/mozbuild/test/frontend/test_emitter.py
+++ b/python/mozbuild/mozbuild/test/frontend/test_emitter.py
@@ -129,6 +129,7 @@ class TestEmitterBasic(unittest.TestCase):
             ASFILES=['fans.asm', 'tans.s'],
             CMMSRCS=['fans.mm', 'tans.mm'],
             CSRCS=['fans.c', 'tans.c'],
+            CPP_UNIT_TESTS=['foo.cpp'],
             DEFINES=['-Dfans', '-Dtans'],
             EXTRA_COMPONENTS=['fans.js', 'tans.js'],
             EXTRA_PP_COMPONENTS=['fans.pp.js', 'tans.pp.js'],