diff --git a/src/eval.c b/src/eval.c
index a7f6086..877b3bc 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -3198,9 +3198,12 @@
 	{
 	    int	    flags = evalarg == NULL ? 0 : evalarg->eval_flags;
 
-	    if (**arg == '(')
+	    if ((in_vim9script() ? **arg : *skipwhite(*arg)) == '(')
+	    {
 		// "name(..."  recursive!
+		*arg = skipwhite(*arg);
 		ret = eval_func(arg, evalarg, s, len, rettv, flags, NULL);
+	    }
 	    else if (flags & EVAL_CONSTANT)
 		ret = FAIL;
 	    else if (evaluate)
diff --git a/src/testdir/test_expr.vim b/src/testdir/test_expr.vim
index b4eeea6..cfae760 100644
--- a/src/testdir/test_expr.vim
+++ b/src/testdir/test_expr.vim
@@ -599,6 +599,11 @@
   call assert_fails("let v = -{}", 'E728:')
 endfunc
 
+func Test_white_in_function_call()
+  let text = substitute ( 'some text' , 't' , 'T' , 'g' )
+  call assert_equal('some TexT', text)
+endfunc
+
 " Test for float value comparison
 func Test_float_compare()
   CheckFeature float
diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index aa705b2..746983d 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -1686,6 +1686,10 @@
   assert_equal([0, 1, 2], --3->range())
 
   call CheckDefFailure(["let x = 'yes'->Echo"], 'E107:')
+  call CheckScriptFailure([
+	"vim9script",
+	"let x = substitute ('x', 'x', 'x', 'x')"
+	], 'E121:')
 enddef
 
 
diff --git a/src/version.c b/src/version.c
index f5eb42b..ba24f69 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1378,
+/**/
     1377,
 /**/
     1376,