--- a/python/mozbuild/mozbuild/code_analysis/mach_commands.py
+++ b/python/mozbuild/mozbuild/code_analysis/mach_commands.py
@@ -2157,28 +2157,34 @@ class StaticAnalysis(MachCommandBase):
                 command.append("-fsyntax-only")
                 command = [
                     re.sub(r'\'-D(.*)="(.*)"\'', r'-D\1="\2"', arg) for arg in command
                 ]
                 commands.append(command)
 
         max_workers = multiprocessing.cpu_count()
 
+        rc = 0
         with concurrent.futures.ThreadPoolExecutor(max_workers=max_workers) as executor:
             futures = []
             for command in commands:
                 futures.append(
                     executor.submit(
                         self.run_process,
                         args=command,
                         cwd=self.topsrcdir,
                         pass_thru=True,
                         ensure_exit_code=False,
                     )
                 )
+            for thread in concurrent.futures.as_completed(futures):
+                if thread.result() != 0:
+                    rc = thread.result()
+
+        return rc
 
     @Command(
         "clang-format",
         category="misc",
         description="Run clang-format on current changes",
     )
     @CommandArgument(
         "--show",

--- a/taskcluster/ci/source-test/clang.yml
+++ b/taskcluster/ci/source-test/clang.yml
@@ -94,8 +94,24 @@ external:
     fetches:
         toolchain:
             - linux64-clang-tidy-external
     worker:
         artifacts:
             - type: file
               name: public/code-review/clang-tidy.json
               path: /builds/worker/clang-tidy.json
+
+non-unified:
+    description: Run syntax test for non-unified build on C/C++ files.
+    treeherder:
+        symbol: cpp(non-unified)
+    attributes:
+        code-review: false
+    run-on-projects: [mozilla-central]
+    run:
+        cwd: '{checkout}'
+        command: >-
+            source taskcluster/scripts/misc/source-test-clang-setup.sh &&
+            taskcluster/scripts/misc/source-test-clang-non-unified.sh
+    fetches:
+        toolchain:
+            - linux64-clang-tidy

new file mode 100755
--- /dev/null
+++ b/taskcluster/scripts/misc/source-test-clang-non-unified.sh
@@ -0,0 +1,13 @@
+#!/bin/bash
+
+NON_UNIFIED_CFG=$GECKO_PATH/build/non-unified-compat
+
+while IFS= read -r directory
+do
+  echo "Running non-unified compile test for: $directory"
+  ./mach static-analysis check-syntax $directory
+  if [ $? -ne 0 ]; then
+    # If failure do not continue with the rest of the directories
+    exit 1
+  fi
+done < $NON_UNIFIED_CFG

--- a/taskcluster/scripts/misc/source-test-clang-setup.sh
+++ b/taskcluster/scripts/misc/source-test-clang-setup.sh
@@ -11,13 +11,15 @@ export LD_LIBRARY_PATH=$MOZ_FETCHES_DIR/
 export MOZCONFIG=$GECKO_PATH/mozconfig
 
 # Add to mozconfig all the appropriate options
 cat <<EOT >> $MOZCONFIG
 # Enable debug mode
 ac_add_options --enable-debug
 # Enable GC zeal, a testing and debugging feature that helps find GC-related bugs in JSAPI applications.
 ac_add_options --enable-gczeal
+# Do not treat warnings as errors
+ac_add_options --disable-warnings-as-errors
 EOT
 
 # Mach lookup clang-tidy in clang-tools
 mkdir -p $MOZBUILD_STATE_PATH/clang-tools
 ln -s $MOZ_FETCHES_DIR/clang-tidy $MOZBUILD_STATE_PATH/clang-tools/clang-tidy