--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -3168,6 +3168,7 @@ set_var_const(
     hashtab_T	*ht;
     int		is_script_local;
     int		vim9script = in_vim9script();
+    int		var_in_vim9script;
 
     ht = find_var_ht(name, &varname);
     if (ht == NULL || *varname == NUL)
@@ -3186,6 +3187,7 @@ set_var_const(
 	vim9_declare_error(name);
 	goto failed;
     }
+    var_in_vim9script = is_script_local && current_script_is_vim9();
 
     di = find_var_in_ht(ht, 0, varname, TRUE);
 
@@ -3217,7 +3219,7 @@ set_var_const(
 		goto failed;
 	    }
 
-	    if (is_script_local && vim9script)
+	    if (var_in_vim9script)
 	    {
 		where_T where;
 
@@ -3244,7 +3246,7 @@ set_var_const(
 
 	    // A Vim9 script-local variable is also present in sn_all_vars and
 	    // sn_var_vals.  It may set "type" from "tv".
-	    if (is_script_local && vim9script)
+	    if (var_in_vim9script)
 		update_vim9_script_var(FALSE, di, flags, tv, &type);
 	}
 
@@ -3308,7 +3310,7 @@ set_var_const(
 	}
 
 	// add a new variable
-	if (vim9script && is_script_local && (flags & ASSIGN_NO_DECL))
+	if (var_in_vim9script && (flags & ASSIGN_NO_DECL))
 	{
 	    semsg(_(e_unknown_variable_str), name);
 	    goto failed;
@@ -3342,7 +3344,7 @@ set_var_const(
 
 	// A Vim9 script-local variable is also added to sn_all_vars and
 	// sn_var_vals. It may set "type" from "tv".
-	if (is_script_local && vim9script)
+	if (var_in_vim9script)
 	    update_vim9_script_var(TRUE, di, flags, tv, &type);
     }
 

--- a/src/proto/vim9script.pro
+++ b/src/proto/vim9script.pro
@@ -1,5 +1,6 @@
 /* vim9script.c */
 int in_vim9script(void);
+int current_script_is_vim9(void);
 void ex_vim9script(exarg_T *eap);
 int not_in_vim9(exarg_T *eap);
 int vim9_bad_comment(char_u *p);

--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -3220,6 +3220,35 @@ def Test_source_vim9_from_legacy()
   delete('Xvim9_script.vim')
 enddef
 
+def Test_declare_script_in_func()
+  var lines =<< trim END
+      vim9script
+      func Declare()
+        let s:local = 123
+      endfunc
+      Declare()
+      assert_equal(123, local)
+
+      var error: string
+      try
+        local = 'asdf'
+      catch
+        error = v:exception
+      endtry
+      assert_match('E1012: Type mismatch; expected number but got string', error)
+
+      lockvar local
+      try
+        local = 999
+      catch
+        error = v:exception
+      endtry
+      assert_match('E741: Value is locked: local', error)
+  END
+  CheckScriptSuccess(lines)
+enddef
+        
+
 func Test_vim9script_not_global()
   " check that items defined in Vim9 script are script-local, not global
   let vim9lines =<< trim END

--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@ static char *(features[]) =
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2680,
+/**/
     2679,
 /**/
     2678,

--- a/src/vim9script.c
+++ b/src/vim9script.c
@@ -17,17 +17,33 @@
 # include "vim9.h"
 #endif
 
+/*
+ * Return TRUE when currently using Vim9 script syntax.
+ * Does not go up the stack, a ":function" inside vim9script uses legacy
+ * syntax.
+ */
     int
 in_vim9script(void)
 {
-    // Do not go up the stack, a ":function" inside vim9script uses legacy
-    // syntax.  "sc_version" is also set when compiling a ":def" function in
-    // legacy script.
+    // "sc_version" is also set when compiling a ":def" function in legacy
+    // script.
     return current_sctx.sc_version == SCRIPT_VERSION_VIM9
 		|| (cmdmod.cmod_flags & CMOD_VIM9CMD);
 }
 
 /*
+ * Return TRUE if the current script is Vim9 script.
+ * This also returns TRUE in a legacy function in a Vim9 script.
+ */
+    int
+current_script_is_vim9(void)
+{
+    return SCRIPT_ID_VALID(current_sctx.sc_sid)
+	    && SCRIPT_ITEM(current_sctx.sc_sid)->sn_version
+						       == SCRIPT_VERSION_VIM9;
+}
+
+/*
  * ":vim9script".
  */
     void