diff --git a/builtinImpl.mpl b/builtinImpl.mpl
index 472606d..0ca8231 100644
--- a/builtinImpl.mpl
+++ b/builtinImpl.mpl
@@ -1328,6 +1328,13 @@ staticityOfBinResult: [
   ] when
 ] "mplBuiltinIsConst" @declareBuiltin ucall
 
+[
+  refToVar: @processor @block pop;
+  processor compilable [
+    refToVar staticityOfVar Dirty = makeValuePair VarCond @processor @block createVariable Static @processor @block makeStaticity @processor @block createPlainIR @block push
+  ] when
+] "mplBuiltinIsDirty" @declareBuiltin ucall
+
 [
   refToVar: @processor @block pop;
   processor compilable [
diff --git a/builtins.mpl b/builtins.mpl
index 9041829..26e6d09 100644
--- a/builtins.mpl
+++ b/builtins.mpl
@@ -65,6 +65,7 @@ builtins: (
   {name: "is"                            ; impl: @mplBuiltinIs                      ;}
   {name: "isCombined"                    ; impl: @mplBuiltinIsCombined              ;}
   {name: "isConst"                       ; impl: @mplBuiltinIsConst                 ;}
+  {name: "isDirty"                       ; impl: @mplBuiltinIsDirty                 ;}
   {name: "isDynamic"                     ; impl: @mplBuiltinIsDynamic               ;}
   {name: "isRef"                         ; impl: @mplBuiltinIsRef                   ;}
   {name: "isStatic"                      ; impl: @mplBuiltinIsStatic                ;}