diff --git a/src/fun/parser.rs b/src/fun/parser.rs
index 8624d643..0ba98453 100644
--- a/src/fun/parser.rs
+++ b/src/fun/parser.rs
@@ -133,12 +133,12 @@ impl<'a> TermParser<'a> {
             def.rules.push(rule);
           } else {
             // Trying to add a new rule to a previous definition, coming from a different rule.
-            let msg = format!("Redefinition of function '{name}'");
+            let msg = self.redefinition_of_function_msg(builtin, &name);
             return self.with_ctx(Err(msg), ini_idx, end_idx);
           }
         } else {
           // Trying to add a new rule to a previous definition, coming from another kind of top-level.
-          let msg = format!("Redefinition of function '{name}'");
+          let msg = self.redefinition_of_function_msg(builtin, &name);
           return self.with_ctx(Err(msg), ini_idx, end_idx);
         }
       } else {
@@ -1234,4 +1234,12 @@ pub trait ParserCommons<'a>: Parser<'a> {
     self.consume_exactly("`")?;
     Ok(result)
   }
+
+  fn redefinition_of_function_msg(&self, builtin: bool, function_name: &str) -> String {
+    if builtin {
+      format!("Redefinition of builtin (function) '{function_name}'.")
+    } else {
+      format!("Redefinition of function '{function_name}'.")
+    }
+  }
 }
diff --git a/src/imp/parser.rs b/src/imp/parser.rs
index 45ee1a7a..7fb9e3a3 100644
--- a/src/imp/parser.rs
+++ b/src/imp/parser.rs
@@ -1069,8 +1069,8 @@ impl<'a> PyParser<'a> {
     end_idx: usize,
     builtin: bool,
   ) -> ParseResult<()> {
-    if book.defs.contains_key(&def.name) {
-      let msg = format!("Redefinition of function '{}'.", def.name);
+    if let Some(def) = book.defs.get(&def.name) {
+      let msg = self.redefinition_of_function_msg(def.builtin, &def.name);
       return self.with_ctx(Err(msg), ini_idx, end_idx);
     }
     if book.ctrs.contains_key(&def.name) {
diff --git a/tests/golden_tests/parse_file/redefinition_builtin.bend b/tests/golden_tests/parse_file/redefinition_builtin.bend
new file mode 100644
index 00000000..5dae112f
--- /dev/null
+++ b/tests/golden_tests/parse_file/redefinition_builtin.bend
@@ -0,0 +1,5 @@
+def Map/get(m):
+  return m
+
+def main:
+  return *(*(*(*(*(*)))))
diff --git a/tests/snapshots/parse_file__redefinition_builtin.bend.snap b/tests/snapshots/parse_file__redefinition_builtin.bend.snap
new file mode 100644
index 00000000..2ea6f62f
--- /dev/null
+++ b/tests/snapshots/parse_file__redefinition_builtin.bend.snap
@@ -0,0 +1,11 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/parse_file/redefinition_builtin.bend
+---
+Errors:
+In tests/golden_tests/parse_file/redefinition_builtin.bend :
+Redefinition of builtin (function) 'Map/get'.
+  1 | def Map/get(m):
+  2 |   return m
+  3 | 
+  4 | def main:
diff --git a/tests/snapshots/parse_file__redefinition_imp_fun.bend.snap b/tests/snapshots/parse_file__redefinition_imp_fun.bend.snap
index e14ae79d..39d574ed 100644
--- a/tests/snapshots/parse_file__redefinition_imp_fun.bend.snap
+++ b/tests/snapshots/parse_file__redefinition_imp_fun.bend.snap
@@ -4,5 +4,5 @@ input_file: tests/golden_tests/parse_file/redefinition_imp_fun.bend
 ---
 Errors:
 In tests/golden_tests/parse_file/redefinition_imp_fun.bend :
-Redefinition of function 'A'
+Redefinition of function 'A'.
   5 | (A) = 1
diff --git a/tests/snapshots/parse_file__redefinition_with_def_between.bend.snap b/tests/snapshots/parse_file__redefinition_with_def_between.bend.snap
index aca21a52..25c12461 100644
--- a/tests/snapshots/parse_file__redefinition_with_def_between.bend.snap
+++ b/tests/snapshots/parse_file__redefinition_with_def_between.bend.snap
@@ -4,5 +4,5 @@ input_file: tests/golden_tests/parse_file/redefinition_with_def_between.bend
 ---
 Errors:
 In tests/golden_tests/parse_file/redefinition_with_def_between.bend :
-Redefinition of function 'A'
+Redefinition of function 'A'.
    4 | (A) = @x x
diff --git a/tests/snapshots/parse_file__redefinition_with_object_between.bend.snap b/tests/snapshots/parse_file__redefinition_with_object_between.bend.snap
index a95e8146..707c7f13 100644
--- a/tests/snapshots/parse_file__redefinition_with_object_between.bend.snap
+++ b/tests/snapshots/parse_file__redefinition_with_object_between.bend.snap
@@ -4,5 +4,5 @@ input_file: tests/golden_tests/parse_file/redefinition_with_object_between.bend
 ---
 Errors:
 In tests/golden_tests/parse_file/redefinition_with_object_between.bend :
-Redefinition of function 'A'
+Redefinition of function 'A'.
   3 | A = 1
diff --git a/tests/snapshots/parse_file__redefinition_with_type_between.bend.snap b/tests/snapshots/parse_file__redefinition_with_type_between.bend.snap
index 264ad129..ccdc4328 100644
--- a/tests/snapshots/parse_file__redefinition_with_type_between.bend.snap
+++ b/tests/snapshots/parse_file__redefinition_with_type_between.bend.snap
@@ -4,5 +4,5 @@ input_file: tests/golden_tests/parse_file/redefinition_with_type_between.bend
 ---
 Errors:
 In tests/golden_tests/parse_file/redefinition_with_type_between.bend :
-Redefinition of function 'A'
+Redefinition of function 'A'.
   3 | A = 1