diff --git a/src/parser.cpp b/src/parser.cpp
index c8c53e81b7..275fa90167 100644
--- a/src/parser.cpp
+++ b/src/parser.cpp
@@ -689,6 +689,9 @@ static AstNode *ast_parse_top_level_decl(ParseContext *pc, VisibMod visib_mod, B
 
             AstNode *res = fn_proto;
             if (body != nullptr) {
+                if (fn_proto->data.fn_proto.is_extern) {
+                    ast_error(pc, first, "Extern functions have no body");
+                }
                 res = ast_create_node_copy_line_info(pc, NodeTypeFnDef, fn_proto);
                 res->data.fn_def.fn_proto = fn_proto;
                 res->data.fn_def.body = body;
diff --git a/test/compile_errors.zig b/test/compile_errors.zig
index 2c52ee2c67..dd688e6c10 100644
--- a/test/compile_errors.zig
+++ b/test/compile_errors.zig
@@ -12,6 +12,14 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
         "tmp.zig:1:11: error: use of undeclared identifier 'B'",
     });
 
+    cases.addTest("reject extern function definitions with body",
+        \\extern "c" fn definitelyNotInLibC(a: i32, b: i32) i32 {
+        \\    return a + b;
+        \\}
+    , &[_][]const u8{
+        "tmp.zig:1:1: error: Extern functions have no body",
+    });
+
     cases.addTest("duplicate field in anonymous struct literal",
         \\export fn entry() void {
         \\    const anon = .{