diff --git a/lightstep-haskell.cabal b/lightstep-haskell.cabal
--- a/lightstep-haskell.cabal
+++ b/lightstep-haskell.cabal
@@ -1,7 +1,7 @@
 cabal-version: 2.4
 
 name:           lightstep-haskell
-version:        0.4.4
+version:        0.4.5
 synopsis:       LightStep OpenTracing client library
 description:    LightStep OpenTracing client library. Uses GRPC transport via proto-lens.
 category:       Tools
diff --git a/src/LightStep/HighLevel/IO.hs b/src/LightStep/HighLevel/IO.hs
--- a/src/LightStep/HighLevel/IO.hs
+++ b/src/LightStep/HighLevel/IO.hs
@@ -67,7 +67,9 @@
       globalSharedMutableSpanStacks
       ( \stacks ->
           let (sp : sps) = stacks HM.! tId
-              !stacks' = HM.insert tId sps stacks
+              !stacks' = case sps of
+                [] -> HM.delete tId stacks
+                _ -> HM.insert tId sps stacks
            in pure (stacks', sp)
       )
   sp' <- finishSpan sp