diff --git a/src/eval.c b/src/eval.c
index df5b842..69be2af 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -3725,6 +3725,7 @@
     int		range = FALSE;
     char_u	*key = NULL;
     int		keylen = -1;
+    int		vim9 = in_vim9script();
 
     if (check_can_index(rettv, evaluate, verbose) == FAIL)
 	return FAIL;
@@ -3755,6 +3756,12 @@
 	    empty1 = TRUE;
 	else if (eval1(arg, &var1, evalarg) == FAIL)	// recursive!
 	    return FAIL;
+	else if (vim9 && **arg == ':')
+	{
+	    semsg(_(e_white_space_required_before_and_after_str), ":");
+	    clear_tv(&var1);
+	    return FAIL;
+	}
 	else if (evaluate && tv_get_string_chk(&var1) == NULL)
 	{
 	    // not a number or string
@@ -3769,7 +3776,15 @@
 	if (**arg == ':')
 	{
 	    range = TRUE;
-	    *arg = skipwhite_and_linebreak(*arg + 1, evalarg);
+	    ++*arg;
+	    if (!IS_WHITE_OR_NUL(**arg) && **arg != ']')
+	    {
+		semsg(_(e_white_space_required_before_and_after_str), ":");
+		if (!empty1)
+		    clear_tv(&var1);
+		return FAIL;
+	    }
+	    *arg = skipwhite_and_linebreak(*arg, evalarg);
 	    if (**arg == ']')
 		empty2 = TRUE;
 	    else if (eval1(arg, &var2, evalarg) == FAIL)	// recursive!
diff --git a/src/testdir/test_vim9_disassemble.vim b/src/testdir/test_vim9_disassemble.vim
index c5b546a..509a575 100644
--- a/src/testdir/test_vim9_disassemble.vim
+++ b/src/testdir/test_vim9_disassemble.vim
@@ -1285,7 +1285,7 @@
 
 def StringSlice(): string
   var s = "abcd"
-  var res = s[1:8]
+  var res = s[1 : 8]
   return res
 enddef
 
@@ -1295,7 +1295,7 @@
         'var s = "abcd"\_s*' ..
         '\d PUSHS "abcd"\_s*' ..
         '\d STORE $0\_s*' ..
-        'var res = s\[1:8]\_s*' ..
+        'var res = s\[1 : 8]\_s*' ..
         '\d LOAD $0\_s*' ..
         '\d PUSHNR 1\_s*' ..
         '\d PUSHNR 8\_s*' ..
@@ -1331,7 +1331,7 @@
 
 def ListSlice(): list<number>
   var l = [1, 2, 3]
-  var res = l[1:8]
+  var res = l[1 : 8]
   return res
 enddef
 
@@ -1344,7 +1344,7 @@
         '\d PUSHNR 3\_s*' ..
         '\d NEWLIST size 3\_s*' ..
         '\d STORE $0\_s*' ..
-        'var res = l\[1:8]\_s*' ..
+        'var res = l\[1 : 8]\_s*' ..
         '\d LOAD $0\_s*' ..
         '\d PUSHNR 1\_s*' ..
         '\d PUSHNR 8\_s*' ..
@@ -1405,14 +1405,14 @@
 enddef
 
 def AnySlice(): list<number>
-  var res = g:somelist[1:3]
+  var res = g:somelist[1 : 3]
   return res
 enddef
 
 def Test_disassemble_any_slice()
   var instr = execute('disassemble AnySlice')
   assert_match('AnySlice\_s*' ..
-        'var res = g:somelist\[1:3\]\_s*' ..
+        'var res = g:somelist\[1 : 3\]\_s*' ..
         '\d LOADG g:somelist\_s*' ..
         '\d PUSHNR 1\_s*' ..
         '\d PUSHNR 3\_s*' ..
diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index 9373db2..4998471 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -1718,6 +1718,15 @@
       Main()
   END
   CheckScriptFailure(lines, 'E1127:')
+
+  lines =<< trim END
+      var numbers = [1, 2, 3, 4]
+      var a = 1
+      var b = 2
+  END
+  CheckDefAndScriptFailure(lines + ['echo numbers[1:b]'], 'E1004:', 4)
+  CheckDefAndScriptFailure(lines + ['echo numbers[1: b]'], 'E1004:', 4)
+  CheckDefAndScriptFailure(lines + ['echo numbers[a :b]'], 'E1004:', 4)
 enddef
 
 def Test_expr7_list_vim9script()
@@ -2274,13 +2283,13 @@
     assert_equal('', g:teststring[-1])
     assert_equal('', g:teststring[99])
 
-    assert_equal('b', g:teststring[1:1])
-    assert_equal('bcdef', g:teststring[1:])
-    assert_equal('abcd', g:teststring[:3])
-    assert_equal('cdef', g:teststring[-4:])
-    assert_equal('abcdef', g:teststring[-9:])
-    assert_equal('abcd', g:teststring[:-3])
-    assert_equal('', g:teststring[:-9])
+    assert_equal('b', g:teststring[1 : 1])
+    assert_equal('bcdef', g:teststring[1 :])
+    assert_equal('abcd', g:teststring[: 3])
+    assert_equal('cdef', g:teststring[-4 :])
+    assert_equal('abcdef', g:teststring[-9 :])
+    assert_equal('abcd', g:teststring[: -3])
+    assert_equal('', g:teststring[: -9])
 
     # blob index cannot be out of range
     g:testblob = 0z01ab
@@ -2290,13 +2299,13 @@
     assert_equal(0x01, g:testblob[-2])
 
     # blob slice accepts out of range
-    assert_equal(0z01ab, g:testblob[0:1])
-    assert_equal(0z01, g:testblob[0:0])
-    assert_equal(0z01, g:testblob[-2:-2])
-    assert_equal(0zab, g:testblob[1:1])
-    assert_equal(0zab, g:testblob[-1:-1])
-    assert_equal(0z, g:testblob[2:2])
-    assert_equal(0z, g:testblob[0:-3])
+    assert_equal(0z01ab, g:testblob[0 : 1])
+    assert_equal(0z01, g:testblob[0 : 0])
+    assert_equal(0z01, g:testblob[-2 : -2])
+    assert_equal(0zab, g:testblob[1 : 1])
+    assert_equal(0zab, g:testblob[-1 : -1])
+    assert_equal(0z, g:testblob[2 : 2])
+    assert_equal(0z, g:testblob[0 : -3])
 
     # list index cannot be out of range
     g:testlist = [0, 1, 2, 3]
@@ -2308,19 +2317,19 @@
     assert_equal(1, g:testlist[g:theone])
 
     # list slice accepts out of range
-    assert_equal([0], g:testlist[0:0])
-    assert_equal([3], g:testlist[3:3])
-    assert_equal([0, 1], g:testlist[0:1])
-    assert_equal([0, 1, 2, 3], g:testlist[0:3])
-    assert_equal([0, 1, 2, 3], g:testlist[0:9])
-    assert_equal([], g:testlist[-1:1])
-    assert_equal([1], g:testlist[-3:1])
-    assert_equal([0, 1], g:testlist[-4:1])
-    assert_equal([0, 1], g:testlist[-9:1])
-    assert_equal([1, 2, 3], g:testlist[1:-1])
-    assert_equal([1], g:testlist[1:-3])
-    assert_equal([], g:testlist[1:-4])
-    assert_equal([], g:testlist[1:-9])
+    assert_equal([0], g:testlist[0 : 0])
+    assert_equal([3], g:testlist[3 : 3])
+    assert_equal([0, 1], g:testlist[0 : 1])
+    assert_equal([0, 1, 2, 3], g:testlist[0 : 3])
+    assert_equal([0, 1, 2, 3], g:testlist[0 : 9])
+    assert_equal([], g:testlist[-1 : 1])
+    assert_equal([1], g:testlist[-3 : 1])
+    assert_equal([0, 1], g:testlist[-4 : 1])
+    assert_equal([0, 1], g:testlist[-9 : 1])
+    assert_equal([1, 2, 3], g:testlist[1 : -1])
+    assert_equal([1], g:testlist[1 : -3])
+    assert_equal([], g:testlist[1 : -4])
+    assert_equal([], g:testlist[1 : -9])
 
     g:testdict = {a: 1, b: 2}
     assert_equal(1, g:testdict['a'])
@@ -2340,8 +2349,8 @@
   CheckDefExecFailure(['echo g:testlist[-5]'], 'E684:', 1)
   CheckScriptFailure(['vim9script', 'echo g:testlist[-5]'], 'E684:', 2)
 
-  CheckDefExecFailure(['echo g:testdict["a":"b"]'], 'E719:', 1)
-  CheckScriptFailure(['vim9script', 'echo g:testdict["a":"b"]'], 'E719:', 2)
+  CheckDefExecFailure(['echo g:testdict["a" : "b"]'], 'E719:', 1)
+  CheckScriptFailure(['vim9script', 'echo g:testdict["a" : "b"]'], 'E719:', 2)
   CheckDefExecFailure(['echo g:testdict[1]'], 'E716:', 1)
   CheckScriptFailure(['vim9script', 'echo g:testdict[1]'], 'E716:', 2)
 
@@ -2746,45 +2755,45 @@
     assert_equal('', text[6])
     assert_equal('', text[999])
 
-    assert_equal('ábçdëf', text[0:-1])
-    assert_equal('ábçdëf', text[0 :-1])
-    assert_equal('ábçdëf', text[0: -1])
+    assert_equal('ábçdëf', text[0 : -1])
+    assert_equal('ábçdëf', text[0 : -1])
+    assert_equal('ábçdëf', text[0 : -1])
     assert_equal('ábçdëf', text[0 : -1])
     assert_equal('ábçdëf', text[0
-                  :-1])
-    assert_equal('ábçdëf', text[0:
+                  : -1])
+    assert_equal('ábçdëf', text[0 :
                   -1])
     assert_equal('ábçdëf', text[0 : -1
                   ])
-    assert_equal('bçdëf', text[1:-1])
-    assert_equal('çdëf', text[2:-1])
-    assert_equal('dëf', text[3:-1])
-    assert_equal('ëf', text[4:-1])
-    assert_equal('f', text[5:-1])
-    assert_equal('', text[6:-1])
-    assert_equal('', text[999:-1])
+    assert_equal('bçdëf', text[1 : -1])
+    assert_equal('çdëf', text[2 : -1])
+    assert_equal('dëf', text[3 : -1])
+    assert_equal('ëf', text[4 : -1])
+    assert_equal('f', text[5 : -1])
+    assert_equal('', text[6 : -1])
+    assert_equal('', text[999 : -1])
 
-    assert_equal('ábçd', text[:3])
-    assert_equal('bçdëf', text[1:])
+    assert_equal('ábçd', text[: 3])
+    assert_equal('bçdëf', text[1 :])
     assert_equal('ábçdëf', text[:])
   END
   CheckDefSuccess(lines)
   CheckScriptSuccess(['vim9script'] + lines)
 
   lines =<< trim END
-      var d = 'asdf'[1:
+      var d = 'asdf'[1 :
   END
   CheckDefFailure(lines, 'E1097:', 3)
   lines =<< trim END
-      var d = 'asdf'[1:xxx]
+      var d = 'asdf'[1 : xxx]
   END
   CheckDefFailure(lines, 'E1001:', 1)
   lines =<< trim END
-      var d = 'asdf'[1:2
+      var d = 'asdf'[1 : 2
   END
   CheckDefFailure(lines, 'E1097:', 3)
   lines =<< trim END
-      var d = 'asdf'[1:2
+      var d = 'asdf'[1 : 2
       echo d
   END
   CheckDefFailure(lines, 'E111:', 2)
@@ -2794,12 +2803,12 @@
   END
   CheckDefFailure(lines, 'E1012: Type mismatch; expected number but got string', 1)
   lines =<< trim END
-      var d = 'asdf'['1':2]
+      var d = 'asdf'['1' : 2]
       echo d
   END
   CheckDefFailure(lines, 'E1012: Type mismatch; expected number but got string', 1)
   lines =<< trim END
-      var d = 'asdf'[1:'2']
+      var d = 'asdf'[1 : '2']
       echo d
   END
   CheckDefFailure(lines, 'E1012: Type mismatch; expected number but got string', 1)
@@ -2813,22 +2822,22 @@
     assert_equal(4, list[-1])
     assert_equal(0, list[-5])
 
-    assert_equal([0, 1, 2, 3, 4], list[0:4])
+    assert_equal([0, 1, 2, 3, 4], list[0 : 4])
     assert_equal([0, 1, 2, 3, 4], list[:])
-    assert_equal([1, 2, 3, 4], list[1:])
-    assert_equal([2, 3, 4], list[2:-1])
-    assert_equal([4], list[4:-1])
-    assert_equal([], list[5:-1])
-    assert_equal([], list[999:-1])
-    assert_equal([1, 2, 3, 4], list[g:theone:g:thefour])
+    assert_equal([1, 2, 3, 4], list[1 :])
+    assert_equal([2, 3, 4], list[2 : -1])
+    assert_equal([4], list[4 : -1])
+    assert_equal([], list[5 : -1])
+    assert_equal([], list[999 : -1])
+    assert_equal([1, 2, 3, 4], list[g:theone : g:thefour])
 
-    assert_equal([0, 1, 2, 3], list[0:3])
-    assert_equal([0], list[0:0])
-    assert_equal([0, 1, 2, 3, 4], list[0:-1])
-    assert_equal([0, 1, 2], list[0:-3])
-    assert_equal([0], list[0:-5])
-    assert_equal([], list[0:-6])
-    assert_equal([], list[0:-99])
+    assert_equal([0, 1, 2, 3], list[0 : 3])
+    assert_equal([0], list[0 : 0])
+    assert_equal([0, 1, 2, 3, 4], list[0 : -1])
+    assert_equal([0, 1, 2], list[0 : -3])
+    assert_equal([0], list[0 : -5])
+    assert_equal([], list[0 : -6])
+    assert_equal([], list[0 : -99])
   END
   CheckDefSuccess(lines)
   CheckScriptSuccess(['vim9script'] + lines)
diff --git a/src/version.c b/src/version.c
index d78ef0f..a74a5d9 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2250,
+/**/
     2249,
 /**/
     2248,
diff --git a/src/vim9compile.c b/src/vim9compile.c
index eb93dff..6ef2b5e 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -3695,19 +3695,33 @@
 	    if (may_get_next_line_error(p, arg, cctx) == FAIL)
 		return FAIL;
 	    if (**arg == ':')
+	    {
 		// missing first index is equal to zero
 		generate_PUSHNR(cctx, 0);
+	    }
 	    else
 	    {
 		if (compile_expr0(arg, cctx) == FAIL)
 		    return FAIL;
+		if (**arg == ':')
+		{
+		    semsg(_(e_white_space_required_before_and_after_str), ":");
+		    return FAIL;
+		}
 		if (may_get_next_line_error(p, arg, cctx) == FAIL)
 		    return FAIL;
 		*arg = skipwhite(*arg);
 	    }
 	    if (**arg == ':')
 	    {
-		*arg = skipwhite(*arg + 1);
+		is_slice = TRUE;
+		++*arg;
+		if (!IS_WHITE_OR_NUL(**arg) && **arg != ']')
+		{
+		    semsg(_(e_white_space_required_before_and_after_str), ":");
+		    return FAIL;
+		}
+		*arg = skipwhite(*arg);
 		if (may_get_next_line_error(p, arg, cctx) == FAIL)
 		    return FAIL;
 		if (**arg == ']')
@@ -3721,7 +3735,6 @@
 			return FAIL;
 		    *arg = skipwhite(*arg);
 		}
-		is_slice = TRUE;
 	    }
 
 	    if (**arg != ']')