diff --git a/tools/widl/parser.l b/tools/widl/parser.l
index 55d246361a7..ef26b42fa42 100644
--- a/tools/widl/parser.l
+++ b/tools/widl/parser.l
@@ -236,6 +236,7 @@ static struct keyword {
 	{"in",				tIN},
 	{"include",			tINCLUDE},
 	{"in_line",			tINLINE},
+	{"input_sync",			tINPUTSYNC},
 	{"int",				tINT},
 /* ... */
 	{"interface",			tINTERFACE},
diff --git a/tools/widl/parser.y b/tools/widl/parser.y
index 69930b3c7d9..8ccc238ef58 100644
--- a/tools/widl/parser.y
+++ b/tools/widl/parser.y
@@ -140,6 +140,7 @@ static type_t std_uhyper = { "MIDL_uhyper" };
 %token tIIDIS
 %token tIMPORT tIMPORTLIB
 %token tIN tINCLUDE tINLINE
+%token tINPUTSYNC
 %token tINT tINT64
 %token tINTERFACE
 %token tLENGTHIS tLIBRARY
@@ -331,6 +332,7 @@ attribute:
 	| tIDEMPOTENT				{ $$ = make_attr(ATTR_IDEMPOTENT); }
 	| tIIDIS '(' ident ')'			{ $$ = make_attrp(ATTR_IIDIS, $3); }
 	| tIN					{ $$ = make_attr(ATTR_IN); }
+	| tINPUTSYNC				{ $$ = make_attr(ATTR_INPUTSYNC); }
 	| tLENGTHIS '(' m_exprs ')'		{ $$ = make_attrp(ATTR_LENGTHIS, $3); }
 	| tLOCAL				{ $$ = make_attr(ATTR_LOCAL); }
 	| tOBJECT				{ $$ = make_attr(ATTR_OBJECT); }
diff --git a/tools/widl/widltypes.h b/tools/widl/widltypes.h
index 5bb503b5c93..c4843f34821 100644
--- a/tools/widl/widltypes.h
+++ b/tools/widl/widltypes.h
@@ -67,6 +67,7 @@ enum attr_type
     ATTR_IDEMPOTENT,
     ATTR_IIDIS,
     ATTR_IN,
+    ATTR_INPUTSYNC,
     ATTR_LENGTHIS,
     ATTR_LOCAL,
     ATTR_OBJECT,