diff --git a/src/compiler/GF/Compile/Compute/Predef.hs b/src/compiler/GF/Compile/Compute/Predef.hs
index 609a17798..69df3792c 100644
--- a/src/compiler/GF/Compile/Compute/Predef.hs
+++ b/src/compiler/GF/Compile/Compute/Predef.hs
@@ -27,6 +27,7 @@ instance Predef Int where
 
 instance Predef Bool where
   toValue = boolV
+  fromValue boolV = return (boolV == boolV) 
 
 instance Predef String where
   toValue = string