diff --git a/core/bootstrap/primitives.factor b/core/bootstrap/primitives.factor
index 87ed5ea529..b9191ac612 100755
--- a/core/bootstrap/primitives.factor
+++ b/core/bootstrap/primitives.factor
@@ -33,6 +33,7 @@ H{ } clone sub-primitives set
 ! Bring up a bare cross-compiling vocabulary.
 "syntax" vocab vocab-words bootstrap-syntax set
 H{ } clone dictionary set
+H{ } clone new-classes set
 H{ } clone changed-definitions set
 H{ } clone forgotten-definitions set
 H{ } clone root-cache set
diff --git a/core/classes/classes.factor b/core/classes/classes.factor
index 610269f8a3..64a8630f36 100755
--- a/core/classes/classes.factor
+++ b/core/classes/classes.factor
@@ -119,7 +119,7 @@ M: sequence implementors [ implementors ] gather ;
 
 : (define-class) ( word props -- )
     >r
-    dup class? [ dup implementors-map+ ] unless
+    dup class? [ dup [ implementors-map+ ] [ new-class ] bi ] unless
     dup reset-class
     dup deferred? [ dup define-symbol ] when
     dup props>>
diff --git a/core/compiler/units/units.factor b/core/compiler/units/units.factor
index a4b10757f6..23e46876fe 100755
--- a/core/compiler/units/units.factor
+++ b/core/compiler/units/units.factor
@@ -135,6 +135,7 @@ SYMBOL: update-tuples-hook
     [
         H{ } clone changed-definitions set
         H{ } clone outdated-tuples set
+        H{ } clone new-classes set
         [ finish-compilation-unit ] [ ] cleanup
     ] with-scope ; inline
 
@@ -143,6 +144,7 @@ SYMBOL: update-tuples-hook
         H{ } clone changed-definitions set
         H{ } clone forgotten-definitions set
         H{ } clone outdated-tuples set
+        H{ } clone new-classes set
         <definitions> new-definitions set
         <definitions> old-definitions set
         [
diff --git a/core/definitions/definitions.factor b/core/definitions/definitions.factor
index 2aa8b894b5..456bb20410 100755
--- a/core/definitions/definitions.factor
+++ b/core/definitions/definitions.factor
@@ -35,6 +35,15 @@ SYMBOL: changed-definitions
     swap changed-definitions get
     [ set-at ] [ no-compilation-unit ] if* ;
 
+SYMBOL: new-classes
+
+: new-class ( word -- )
+    dup new-classes get
+    [ set-at ] [ no-compilation-unit ] if* ;
+
+: new-class? ( word -- ? )
+    new-classes get key? ;
+
 GENERIC: where ( defspec -- loc )
 
 M: object where drop f ;