diff --git a/src/eval.c b/src/eval.c
index a8e388d..bb75528 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -4996,7 +4996,8 @@
     for (p = arg; *p != NUL
 		    && (eval_isnamec(*p)
 			|| (*p == '{' && !vim9script)
-			|| ((flags & FNE_INCL_BR) && (*p == '[' || *p == '.'))
+			|| ((flags & FNE_INCL_BR) && (*p == '['
+					|| (*p == '.' && eval_isnamec1(p[1]))))
 			|| mb_nest != 0
 			|| br_nest != 0); MB_PTR_ADV(p))
     {
diff --git a/src/evalvars.c b/src/evalvars.c
index e2469b0..564c65b 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -698,12 +698,13 @@
     int		i;
     int		var_count = 0;
     int		semicolon = 0;
-    char_u	op[2];
+    char_u	op[4];
     char_u	*argend;
     int		first = TRUE;
     int		concat;
     int		has_assign;
     int		flags = eap->cmdidx == CMD_const ? LET_IS_CONST : 0;
+    int		vim9script = in_vim9script();
 
     // detect Vim9 assignment without ":let" or ":const"
     if (eap->arg == eap->cmd)
@@ -725,11 +726,11 @@
 	// ":let" without "=": list variables
 	if (*arg == '[')
 	    emsg(_(e_invarg));
-	else if (expr[0] == '.')
-	    emsg(_("E985: .= is not supported with script version 2"));
+	else if (expr[0] == '.' && expr[1] == '=')
+	    emsg(_("E985: .= is not supported with script version >= 2"));
 	else if (!ends_excmd2(eap->cmd, arg))
 	{
-	    if (in_vim9script())
+	    if (vim9script)
 	    {
 		// Vim9 declaration ":let var: type"
 		arg = vim9_declare_scriptvar(eap, arg);
@@ -775,6 +776,7 @@
     else
     {
 	evalarg_T   evalarg;
+	int	    len = 1;
 
 	rettv.v_type = VAR_UNKNOWN;
 	i = FAIL;
@@ -787,13 +789,25 @@
 		if (vim_strchr((char_u *)"+-*/%.", *expr) != NULL)
 		{
 		    op[0] = *expr;   // +=, -=, *=, /=, %= or .=
+		    ++len;
 		    if (expr[0] == '.' && expr[1] == '.') // ..=
+		    {
 			++expr;
+			++len;
+		    }
 		}
-		expr = skipwhite(expr + 2);
+		expr += 2;
 	    }
 	    else
-		expr = skipwhite(expr + 1);
+		++expr;
+
+	    if (vim9script && (!VIM_ISWHITE(*argend) || !VIM_ISWHITE(*expr)))
+	    {
+		vim_strncpy(op, expr - len, len);
+		semsg(_(e_white_both), op);
+		i = FAIL;
+	    }
+	    expr = skipwhite(expr);
 
 	    if (eap->skip)
 		++emsg_skip;
@@ -817,7 +831,7 @@
 	else if (i != FAIL)
 	{
 	    (void)ex_let_vars(eap->arg, &rettv, FALSE, semicolon, var_count,
-								 flags, op);
+								    flags, op);
 	    clear_tv(&rettv);
 	}
     }
diff --git a/src/testdir/test_let.vim b/src/testdir/test_let.vim
index 404fe15..9a399e8 100644
--- a/src/testdir/test_let.vim
+++ b/src/testdir/test_let.vim
@@ -293,12 +293,12 @@
   let s = "var"
   let var = 1
   call assert_fails('let var += [1,2]', 'E734:')
-  call assert_fails('let {s}.1 = 2', 'E18:')
+  call assert_fails('let {s}.1 = 2', 'E15:')
   call assert_fails('let a[1] = 5', 'E121:')
   let l = [[1,2]]
   call assert_fails('let l[:][0] = [5]', 'E708:')
   let d = {'k' : 4}
-  call assert_fails('let d.# = 5', 'E713:')
+  call assert_fails('let d.# = 5', 'E488:')
   call assert_fails('let d.m += 5', 'E734:')
   call assert_fails('let m = d[{]', 'E15:')
   let l = [1, 2]
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index 36d7e89..fd572d7 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -318,6 +318,15 @@
   call CheckDefFailure(['let var =234'], 'E1004:')
   call CheckDefFailure(['let var= 234'], 'E1004:')
 
+  call CheckScriptFailure(['vim9script', 'let var=234'], 'E1004:')
+  call CheckScriptFailure(['vim9script', 'let var=234'], "before and after '='")
+  call CheckScriptFailure(['vim9script', 'let var =234'], 'E1004:')
+  call CheckScriptFailure(['vim9script', 'let var= 234'], 'E1004:')
+  call CheckScriptFailure(['vim9script', 'let var = 234', 'var+=234'], 'E1004:')
+  call CheckScriptFailure(['vim9script', 'let var = 234', 'var+=234'], "before and after '+='")
+  call CheckScriptFailure(['vim9script', 'let var = "x"', 'var..="y"'], 'E1004:')
+  call CheckScriptFailure(['vim9script', 'let var = "x"', 'var..="y"'], "before and after '..='")
+
   call CheckDefFailure(['let true = 1'], 'E1034:')
   call CheckDefFailure(['let false = 1'], 'E1034:')
 
diff --git a/src/version.c b/src/version.c
index ed8f6c4..82b5780 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1274,
+/**/
     1273,
 /**/
     1272,