diff --git a/tooling/nargo_fmt/src/visitor/stmt.rs b/tooling/nargo_fmt/src/visitor/stmt.rs
index b414e5ec5c3..44c5dad6b5d 100644
--- a/tooling/nargo_fmt/src/visitor/stmt.rs
+++ b/tooling/nargo_fmt/src/visitor/stmt.rs
@@ -38,7 +38,10 @@ impl super::FmtVisitor<'_> {
 
                     nested_shape.indent.block_indent(self.config);
 
-                    let message = message.map_or(String::new(), |message| format!(", {message}"));
+                    let message = message.map_or(String::new(), |message| {
+                        let message = rewrite::sub_expr(self, nested_shape, message);
+                        format!(", {message}")
+                    });
 
                     let (callee, args) = match kind {
                         ConstrainKind::Assert | ConstrainKind::Constrain => {
diff --git a/tooling/nargo_fmt/tests/expected/assert.nr b/tooling/nargo_fmt/tests/expected/assert.nr
index 1f38e56b799..805e069c9a7 100644
--- a/tooling/nargo_fmt/tests/expected/assert.nr
+++ b/tooling/nargo_fmt/tests/expected/assert.nr
@@ -1,4 +1,5 @@
 fn main(x: Field) {
     assert(x == 0, "with a message");
     assert_eq(x, 1);
+    assert(x, message);
 }
diff --git a/tooling/nargo_fmt/tests/input/assert.nr b/tooling/nargo_fmt/tests/input/assert.nr
index f41e396c041..d0259da0e24 100644
--- a/tooling/nargo_fmt/tests/input/assert.nr
+++ b/tooling/nargo_fmt/tests/input/assert.nr
@@ -4,4 +4,5 @@ fn main(x: Field) {
         x,
         1
     );
+    assert( x, message );
 }