diff --git a/src/plugins/e-acsl/env.ml b/src/plugins/e-acsl/env.ml
index 6c2493c460b1cc917084b88acdcc4b55699a0319..6b6c32680bd9925262bb82e88c92b30097774c68 100644
--- a/src/plugins/e-acsl/env.ml
+++ b/src/plugins/e-acsl/env.ml
@@ -371,7 +371,10 @@ let pop_and_get env stmt ~global_clear where =
 	| _ :: tl ->
 	  match stmt.skind with
 	  | Block { bstmts = [ fst; snd ] } -> extract snd (fst :: acc) tl
-	  | _ -> assert false
+	  | _ ->
+            Kernel.fatal
+              "experting a block containing 2 statements instead of %a"
+              Printer.pp_stmt stmt
       in
       extract stmt [] block.pre_stmts
     in