diff --git a/src/usexp/dune_lexer.mll b/src/usexp/dune_lexer.mll
index 61b471fa..20720132 100644
--- a/src/usexp/dune_lexer.mll
+++ b/src/usexp/dune_lexer.mll
@@ -300,4 +300,4 @@ and template_variable = parse
   }
   | '}' | eof
     { error lexbuf "%{...} forms cannot be empty" }
-  | _ { error lexbuf "This character not allowed inside %{...} forms" }
+  | _ { error lexbuf "This character is not allowed inside %{...} forms" }
diff --git a/test/blackbox-tests/test-cases/quoting/run.t b/test/blackbox-tests/test-cases/quoting/run.t
index 15890bbc..9bd425f6 100644
--- a/test/blackbox-tests/test-cases/quoting/run.t
+++ b/test/blackbox-tests/test-cases/quoting/run.t
@@ -27,10 +27,10 @@ The targets should only be interpreted as a single path when quoted
 
   $ dune build @quoted --root filename-space
   File "dune", line 4, characters 17-18:
-  Error: This character not allowed inside %{...} forms
+  Error: This character is not allowed inside %{...} forms
   [1]
 
   $ dune build @unquoted --root filename-space
   File "dune", line 4, characters 17-18:
-  Error: This character not allowed inside %{...} forms
+  Error: This character is not allowed inside %{...} forms
   [1]