diff --git a/python/mozbuild/mozbuild/frontend/emitter.py b/python/mozbuild/mozbuild/frontend/emitter.py
index 19af243c5d7a..1d5753a39a32 100644
--- a/python/mozbuild/mozbuild/frontend/emitter.py
+++ b/python/mozbuild/mozbuild/frontend/emitter.py
@@ -81,6 +81,7 @@ class TreeMetadataEmitter(object):
             # Makefile.in : moz.build
             ASFILES='ASFILES',
             CSRCS='CSRCS',
+            DEFINES='DEFINES',
             MODULE='MODULE',
             SIMPLE_PROGRAMS='SIMPLE_PROGRAMS',
             XPIDL_FLAGS='XPIDL_FLAGS',
diff --git a/python/mozbuild/mozbuild/frontend/sandbox_symbols.py b/python/mozbuild/mozbuild/frontend/sandbox_symbols.py
index db43b267f1de..b7b3e30fada5 100644
--- a/python/mozbuild/mozbuild/frontend/sandbox_symbols.py
+++ b/python/mozbuild/mozbuild/frontend/sandbox_symbols.py
@@ -72,6 +72,12 @@ VARIABLES = {
         This variable contains a list of C source files to compile.
         """),
 
+    'DEFINES': (StrictOrderingOnAppendList, list, [],
+        """Compiler defines to declare.
+
+        Command line -D flags passed to the compiler.
+        """),
+
     'DIRS': (list, list, [],
         """Child directories to descend into looking for build frontend files.
 
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 28477a684eee..0d5be204b1de 100644
--- a/python/mozbuild/mozbuild/test/backend/data/variable_passthru/moz.build
+++ b/python/mozbuild/mozbuild/test/backend/data/variable_passthru/moz.build
@@ -8,6 +8,9 @@ XPIDL_FLAGS = ['-Idir1', '-Idir2', '-Idir3']
 
 ASFILES = ['bar.s', 'foo.asm']
 
+DEFINES = ['-Dbar', '-Dfoo']
+
+
 SIMPLE_PROGRAMS = ['bar.x', 'foo.x']
 
 CSRCS += ['bar.c', 'foo.c']
diff --git a/python/mozbuild/mozbuild/test/backend/test_recursivemake.py b/python/mozbuild/mozbuild/test/backend/test_recursivemake.py
index 55c7bfcaee22..59906957222f 100644
--- a/python/mozbuild/mozbuild/test/backend/test_recursivemake.py
+++ b/python/mozbuild/mozbuild/test/backend/test_recursivemake.py
@@ -146,6 +146,10 @@ class TestRecursiveMakeBackend(BackendTester):
                 'CSRCS += bar.c',
                 'CSRCS += foo.c',
             ],
+            'DEFINES': [
+                'DEFINES += -Dbar',
+                'DEFINES += -Dfoo',
+            ],
             'SIMPLE_PROGRAMS': [
                 'SIMPLE_PROGRAMS += bar.x',
                 'SIMPLE_PROGRAMS += foo.x',
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 2e98f4097998..f1055de23217 100644
--- a/python/mozbuild/mozbuild/test/frontend/data/variable-passthru/moz.build
+++ b/python/mozbuild/mozbuild/test/frontend/data/variable-passthru/moz.build
@@ -8,6 +8,8 @@ XPIDL_FLAGS += ['-Idir1', '-Idir2', '-Idir3']
 
 ASFILES += ['fans.asm', 'tans.s']
 
+DEFINES=['-Dfans', '-Dtans']
+
 SIMPLE_PROGRAMS += ['fans.x', 'tans.x']
 
 CSRCS += ['fans.c', 'tans.c']
diff --git a/python/mozbuild/mozbuild/test/frontend/test_emitter.py b/python/mozbuild/mozbuild/test/frontend/test_emitter.py
index d1b53673e046..c5a04d077a23 100644
--- a/python/mozbuild/mozbuild/test/frontend/test_emitter.py
+++ b/python/mozbuild/mozbuild/test/frontend/test_emitter.py
@@ -126,8 +126,9 @@ class TestEmitterBasic(unittest.TestCase):
 
         wanted = dict(
             ASFILES=['fans.asm', 'tans.s'],
-            SIMPLE_PROGRAMS=['fans.x', 'tans.x'],
             CSRCS=['fans.c', 'tans.c'],
+            DEFINES=['-Dfans', '-Dtans'],
+            SIMPLE_PROGRAMS=['fans.x', 'tans.x'],
             XPIDLSRCS=['bar.idl', 'biz.idl', 'foo.idl'],
             XPIDL_MODULE='module_name',
             XPIDL_FLAGS=['-Idir1', '-Idir2', '-Idir3'],