diff --git a/spec/compiler/parser/parser_spec.cr b/spec/compiler/parser/parser_spec.cr
index e687500ee2d7..388436e0a6cf 100644
--- a/spec/compiler/parser/parser_spec.cr
+++ b/spec/compiler/parser/parser_spec.cr
@@ -1276,6 +1276,8 @@ describe "Parser" do
 
   it_parses "yield foo do\nend", Yield.new([Call.new(nil, "foo", block: Block.new)] of ASTNode)
 
+  it_parses "x.y=(1).to_s", Call.new("x".call, "y=", Call.new(Expressions.new([1.int32] of ASTNode), "to_s"))
+
   assert_syntax_error "return do\nend", "unexpected token: do"
 
   %w(def macro class struct module fun alias abstract include extend lib).each do |keyword|
diff --git a/src/compiler/crystal/syntax/parser.cr b/src/compiler/crystal/syntax/parser.cr
index b5471454a397..e70132dba792 100644
--- a/src/compiler/crystal/syntax/parser.cr
+++ b/src/compiler/crystal/syntax/parser.cr
@@ -640,10 +640,19 @@ module Crystal
               next_token
 
               if @token.type == :"("
-                next_token_skip_space
-                arg = parse_single_arg
-                check :")"
-                next_token
+                # If we have `f.x=(exp1).a.b.c`, consider it the same as `f.x = (exp1).a.b.c`
+                # and not as `(f.x = exp1).a.b.c` because a difference in space
+                # should not make a difference in semantic (#4399)
+                # The only exception is doing a splat, in which case this can only
+                # be expanded arguments for the call.
+                if current_char == '*'
+                  next_token_skip_space
+                  arg = parse_single_arg
+                  check :")"
+                  next_token
+                else
+                  arg = parse_op_assign_no_control
+                end
               else
                 skip_space_or_newline
                 arg = parse_single_arg