diff --git a/src/cargo/util/toml/mod.rs b/src/cargo/util/toml/mod.rs
index 42851b9d4b6..7c472bf8b2f 100644
--- a/src/cargo/util/toml/mod.rs
+++ b/src/cargo/util/toml/mod.rs
@@ -566,7 +566,7 @@ impl TomlProfile {
 
         if let Some(codegen_backend) = &self.codegen_backend {
             features.require(Feature::codegen_backend())?;
-            if codegen_backend.contains(|c| !c.is_ascii_alphanumeric() && c != '_') {
+            if codegen_backend.contains(|c: char| !c.is_ascii_alphanumeric() && c != '_') {
                 bail!(
                     "`profile.{}.codegen-backend` setting of `{}` is not a valid backend name.",
                     name,