diff --git a/extra/compiler/cfg/gvn/gvn.factor b/extra/compiler/cfg/gvn/gvn.factor
index 56ea3023d2..ef1f2f0cd8 100644
--- a/extra/compiler/cfg/gvn/gvn.factor
+++ b/extra/compiler/cfg/gvn/gvn.factor
@@ -51,7 +51,7 @@ M: array process-instruction
 
 ! FIXME there's going to be trouble with certain rewrites that
 ! modify the cfg / instructions destructively; namely those in
-! alien.factor and slots.factor
+! alien.factor
 
 : value-numbering-iteration ( cfg -- )
     clear-exprs
diff --git a/extra/compiler/cfg/gvn/slots/slots.factor b/extra/compiler/cfg/gvn/slots/slots.factor
index d994e194fb..15a1040edd 100644
--- a/extra/compiler/cfg/gvn/slots/slots.factor
+++ b/extra/compiler/cfg/gvn/slots/slots.factor
@@ -13,7 +13,7 @@ IN: compiler.cfg.gvn.slots
 
 : simplify-slot-addressing ( insn -- insn/f )
     dup simplify-slot-addressing? [
-        dup slot>> vreg>insn
+        clone dup slot>> vreg>insn
         [ src1>> >>slot ]
         [ src2>> over scale>> '[ _ _ shift - ] change-tag ]
         bi