--- a/js/moz.configure
+++ b/js/moz.configure
@@ -16,6 +16,15 @@ def js_standalone(build_project):
 set_define("JS_DEBUG", True, when=moz_debug)
 
 
+@depends(moz_debug)
+def js_debug_defines(moz_debug):
+    if moz_debug:
+        return "-DDEBUG"
+    return ""
+
+set_config("JS_DEBUG_DEFINES", js_debug_defines)
+
+
 # Branding
 # ==============================================================
 option(
--- a/js/src/build/js.pc.in
+++ b/js/src/build/js.pc.in
@@ -11,4 +11,4 @@ Libs: -L${libdir} -l@JS_LIBRARY_NAME@
 # Use -isystem for includes rather than -I, to mark them as "system headers"
 # that don't generate warning diagnostics. For justification, see
 # https://bugzilla.mozilla.org/show_bug.cgi?id=1539036
-Cflags: -isystem ${includedir}/@JS_LIBRARY_NAME@
+Cflags: -isystem ${includedir}/@JS_LIBRARY_NAME@ @JS_DEBUG_DEFINES@