diff --git a/CHANGELOG.md b/CHANGELOG.md
index eb32b4ca..64ec3c81 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,6 @@
 ## Unreleased
 
+* Revert "Speed up input mapping lookup by avoiding rescuing exceptions" from v5.3.0, it caused a regression on dev/test environments with custom inputs.
 * Add support to Ruby 3.3. (no changes required.)
 
 ## 5.3.0
diff --git a/lib/simple_form/form_builder.rb b/lib/simple_form/form_builder.rb
index a5cb4c14..da723cb7 100644
--- a/lib/simple_form/form_builder.rb
+++ b/lib/simple_form/form_builder.rb
@@ -673,7 +673,11 @@ def mapping_override(klass)
     def attempt_mapping(mapping, at)
       return if SimpleForm.inputs_discovery == false && at == Object
 
-      at.const_get(mapping) if at.const_defined?(mapping)
+      begin
+        at.const_get(mapping)
+      rescue NameError => e
+        raise if e.message !~ /#{mapping}$/
+      end
     end
 
     def attempt_mapping_with_custom_namespace(input_name)