diff --git a/build/unix/elfhack/inject/moz.build b/build/unix/elfhack/inject/moz.build
--- a/build/unix/elfhack/inject/moz.build
+++ b/build/unix/elfhack/inject/moz.build
@@ -32,11 +32,11 @@
     idx = 0
     for flag in COMPILE_FLAGS[v]:
         if flag == "-isystem":
             flags.append("".join(COMPILE_FLAGS[v][idx : idx + 2]))
         elif (
-            flag.startswith(("-g", "-m", "-I", "-isystem", "--sysroot="))
+            (flag.startswith(("-g", "-m", "-I", "-isystem", "--sysroot=")) and not flag.startswith("-mllvm"))
             or flag == "-fPIC"
         ):
             flags.append(flag)
         idx += 1
     COMPILE_FLAGS[v] = flags