diff --git a/.release-notes/4054.md b/.release-notes/4054.md
new file mode 100644
index 00000000000..f19a3564621
--- /dev/null
+++ b/.release-notes/4054.md
@@ -0,0 +1,5 @@
+## Fixed parameter names not being checked
+
+In 2018, when we [removed case functions](https://github.com/ponylang/ponyc/pull/2542) from Pony, we also removed the checking to make sure that parameters names were valid.
+
+We've added checking of parameter names to make sure they match the naming rules for parameters in Pony.
diff --git a/src/libponyc/pass/sugar.c b/src/libponyc/pass/sugar.c
index d0ad81f9337..df01579447e 100644
--- a/src/libponyc/pass/sugar.c
+++ b/src/libponyc/pass/sugar.c
@@ -321,6 +321,51 @@ static ast_result_t sugar_typeparam(ast_t* ast)
 }
 
 
+static ast_result_t check_params(pass_opt_t* opt, ast_t* params)
+{
+  pony_assert(params != NULL);
+  ast_result_t result = AST_OK;
+
+  // Check each parameter.
+  for(ast_t* p = ast_child(params); p != NULL; p = ast_sibling(p))
+  {
+    if(ast_id(p) == TK_ELLIPSIS)
+      continue;
+
+    AST_GET_CHILDREN(p, id, type, def_arg);
+
+    if(ast_id(id) != TK_ID)
+    {
+      ast_error(opt->check.errors, p, "expected parameter name");
+      result = AST_ERROR;
+    }
+    else if(!is_name_internal_test(ast_name(id)) && !check_id_param(opt, id))
+    {
+      result = AST_ERROR;
+    }
+
+    if(ast_id(type) == TK_NONE)
+    {
+      ast_error(opt->check.errors, type, "expected parameter type");
+      result = AST_ERROR;
+    }
+  }
+
+  return result;
+}
+
+
+static ast_result_t check_method(pass_opt_t* opt, ast_t* method)
+{
+  pony_assert(method != NULL);
+
+  ast_result_t result = AST_OK;
+  ast_t* params = ast_childidx(method, 3);
+  result = check_params(opt, params);
+
+  return result;
+}
+
 
 static ast_result_t sugar_new(pass_opt_t* opt, ast_t* ast)
 {
@@ -348,7 +393,7 @@ static ast_result_t sugar_new(pass_opt_t* opt, ast_t* ast)
   }
 
   sugar_docstring(ast);
-  return AST_OK;
+  return check_method(opt, ast);
 }
 
 
@@ -367,7 +412,7 @@ static ast_result_t sugar_be(pass_opt_t* opt, ast_t* ast)
   }
 
   sugar_docstring(ast);
-  return AST_OK;
+  return check_method(opt, ast);
 }
 
 
@@ -405,10 +450,9 @@ void fun_defaults(ast_t* ast)
 
 static ast_result_t sugar_fun(pass_opt_t* opt, ast_t* ast)
 {
-  (void)opt;
   fun_defaults(ast);
   sugar_docstring(ast);
-  return AST_OK;
+  return check_method(opt, ast);
 }
 
 
@@ -835,6 +879,9 @@ static ast_result_t sugar_ffi(pass_opt_t* opt, ast_t* ast)
   ast_t* new_id = ast_from_string(id, stringtab_consume(new_name, len + 2));
   ast_replace(&id, new_id);
 
+//  if(ast_id(ast) == TK_FFIDECL)
+//    return check_params(opt, args);
+
   return AST_OK;
 }
 
diff --git a/test/libponyc/sugar.cc b/test/libponyc/sugar.cc
index e60432391da..f8b4c70446d 100644
--- a/test/libponyc/sugar.cc
+++ b/test/libponyc/sugar.cc
@@ -553,7 +553,7 @@ TEST_F(SugarTest, FunctionNoReturnBody)
 }
 
 
-TEST_F(SugarTest, FunctionParamMustBeId)
+TEST_F(SugarTest, MethodParamMustBeId)
 {
   const char* good1 =
     "trait Foo\n"
@@ -561,11 +561,17 @@ TEST_F(SugarTest, FunctionParamMustBeId)
 
   TEST_COMPILE(good1);
 
-  const char* good2 =
+  const char* good1_be =
     "trait Foo\n"
-    "  fun foo(_: U64) => 3";
+    "  be foo(x: U64) => 3";
 
-  TEST_COMPILE(good2);
+  TEST_COMPILE(good1_be);
+
+  const char* good1_new =
+    "class Foo\n"
+    "  new create(x: U64) => 3";
+
+  TEST_COMPILE(good1_new);
 
   const char* bad1 =
     "trait Foo\n"
@@ -573,11 +579,89 @@ TEST_F(SugarTest, FunctionParamMustBeId)
 
   TEST_ERROR(bad1);
 
+  const char* bad1_be =
+    "trait Foo\n"
+    "  be foo(x.y(): U64) => 3";
+
+  TEST_ERROR(bad1_be);
+
+  const char* bad1_new =
+    "class Foo\n"
+    "  new create(x.y(): U64) => 3";
+
+  TEST_ERROR(bad1_new);
+
   const char* bad2 =
     "trait Foo\n"
     "  fun foo($: U64) => 3";
 
   TEST_ERROR(bad2);
+
+  const char* bad2_be =
+    "trait Foo\n"
+    "  be foo($: U64) => 3";
+
+  TEST_ERROR(bad2_be);
+
+  const char* bad2_new =
+    "class Foo\n"
+    "  new create($: U64) => 3";
+
+  TEST_ERROR(bad2_new);
+
+  const char* bad3 =
+    "trait Foo\n"
+    "  fun foo(__: U64) => 3";
+
+  TEST_ERROR(bad3);
+
+  const char* bad3_be =
+    "trait Foo\n"
+    "  be foo(__: U64) => 3";
+
+  TEST_ERROR(bad3_be);
+
+  const char* bad3_new =
+    "class Foo\n"
+    "  new create(__: U64) => 3";
+
+  TEST_ERROR(bad3_new);
+
+  const char* bad4 =
+    "trait Foo\n"
+    "  fun foo(_x: U64) => 3";
+
+  TEST_ERROR(bad4);
+
+  const char* bad4_be =
+    "trait Foo\n"
+    "  be foo(_x: U64) => 3";
+
+  TEST_ERROR(bad4_be);
+
+  const char* bad4_new =
+    "class Foo\n"
+    "  new create(_x: U64) => 3";
+
+  TEST_ERROR(bad4_new);
+
+  const char* bad5 =
+    "trait Foo\n"
+    "  fun foo(_x: U64) => 3";
+
+  TEST_ERROR(bad5);
+
+  const char* bad5_be =
+    "trait Foo\n"
+    "  be foo(_x: U64) => 3";
+
+  TEST_ERROR(bad5_be);
+
+  const char* bad5_new =
+    "class Foo\n"
+    "  new create(_x: U64) => 3";
+
+  TEST_ERROR(bad5_new);
 }