diff --git a/accessible/interfaces/ia2/Makefile.in b/accessible/interfaces/ia2/Makefile.in
index fbe7ebb053972..5ba74a52e4161 100644
--- a/accessible/interfaces/ia2/Makefile.in
+++ b/accessible/interfaces/ia2/Makefile.in
@@ -47,12 +47,6 @@ MIDL_LIBRARIES = \
   IA2Typelib.idl \
   $(NULL)
 
-CSRCS = \
-  dlldata.c \
-  $(MIDL_INTERFACES:%.idl=%_p.c) \
-  $(MIDL_INTERFACES:%.idl=%_i.c) \
-  $(NULL)
-
 MIDL_GENERATED_FILES = \
   dlldata.c \
   $(MIDL_ENUMS:%.idl=%.h) \
diff --git a/accessible/interfaces/ia2/moz.build b/accessible/interfaces/ia2/moz.build
index 9ee45199da0f5..401b682a6fdc7 100644
--- a/accessible/interfaces/ia2/moz.build
+++ b/accessible/interfaces/ia2/moz.build
@@ -84,6 +84,10 @@ GENERATED_FILES += [
     'IA2Typelib.tlb',
 ]
 
+SOURCES += [
+    '!%s' % p for p in GENERATED_FILES if p.endswith('.c')
+]
+
 RCINCLUDE = 'IA2Marshal.rc'
 
 # The Windows MIDL code generator creates things like: