diff --git a/src/Data/Terminfo/Eval.hs b/src/Data/Terminfo/Eval.hs
--- a/src/Data/Terminfo/Eval.hs
+++ b/src/Data/Terminfo/Eval.hs
@@ -166,7 +166,7 @@
     let ( !start_ptr, _ ) = cap_bytes cap
         !src_ptr = start_ptr `plusPtr` offset
         !out_ptr' = out_ptr `plusPtr` next_offset
-    liftIO $! memcpy out_ptr src_ptr byte_count
+    liftIO $! memcpy out_ptr src_ptr (fromIntegral byte_count)
     return $! out_ptr'
 serialize_cap_op out_ptr DecOut = do
     p <- pop
diff --git a/vty.cabal b/vty.cabal
--- a/vty.cabal
+++ b/vty.cabal
@@ -1,5 +1,5 @@
 name:                vty
-version:             4.7.0.18
+version:             4.7.0.20
 license:             BSD3
 license-file:        LICENSE
 author:              AUTHORS