diff --git a/src/proto/vim9type.pro b/src/proto/vim9type.pro
index 1ac3727..90f8791 100644
--- a/src/proto/vim9type.pro
+++ b/src/proto/vim9type.pro
@@ -1,4 +1,5 @@
 /* vim9type.c */
+type_T *alloc_type(garray_T *type_gap);
 void clear_type_list(garray_T *gap);
 type_T *get_list_type(type_T *member_type, garray_T *type_gap);
 type_T *get_dict_type(type_T *member_type, garray_T *type_gap);
diff --git a/src/structs.h b/src/structs.h
index dba9be6..0899ae7 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -1373,6 +1373,7 @@
 
 #define TTFLAG_VARARGS	1	    // func args ends with "..."
 #define TTFLAG_OPTARG	2	    // func arg type with "?"
+#define TTFLAG_BOOL_OK	4	    // can be converted to bool
 
 /*
  * Structure to hold an internal variable without a name.
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index 8d8111a..5712e38 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -45,6 +45,11 @@
   let bool2: bool = false
   assert_equal(v:false, bool2)
 
+  let bool3: bool = 0
+  assert_equal(0, bool3)
+  let bool4: bool = 1
+  assert_equal(1, bool4)
+
   CheckDefFailure(['let x:string'], 'E1069:')
   CheckDefFailure(['let x:string = "x"'], 'E1069:')
   CheckDefFailure(['let a:string = "x"'], 'E1069:')
diff --git a/src/version.c b/src/version.c
index 4f7de31..7390d39 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1641,
+/**/
     1640,
 /**/
     1639,
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 8b1dcd5..f88f3a3 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -751,12 +751,25 @@
 generate_PUSHNR(cctx_T *cctx, varnumber_T number)
 {
     isn_T	*isn;
+    garray_T	*stack = &cctx->ctx_type_stack;
 
     RETURN_OK_IF_SKIP(cctx);
     if ((isn = generate_instr_type(cctx, ISN_PUSHNR, &t_number)) == NULL)
 	return FAIL;
     isn->isn_arg.number = number;
 
+    if (number == 0 || number == 1)
+    {
+	type_T	*type = alloc_type(cctx->ctx_type_list);
+
+	// A 0 or 1 number can also be used as a bool.
+	if (type != NULL)
+	{
+	    type->tt_type = VAR_NUMBER;
+	    type->tt_flags = TTFLAG_BOOL_OK;
+	    ((type_T **)stack->ga_data)[stack->ga_len - 1] = type;
+	}
+    }
     return OK;
 }
 
diff --git a/src/vim9type.c b/src/vim9type.c
index 29466d0..4f4876d 100644
--- a/src/vim9type.c
+++ b/src/vim9type.c
@@ -24,7 +24,7 @@
  * Allocate memory for a type_T and add the pointer to type_gap, so that it can
  * be freed later.
  */
-    static type_T *
+    type_T *
 alloc_type(garray_T *type_gap)
 {
     type_T *type;
@@ -359,6 +359,10 @@
     {
 	if (expected->tt_type != actual->tt_type)
 	{
+	    if (expected->tt_type == VAR_BOOL && actual->tt_type == VAR_NUMBER
+					&& (actual->tt_flags & TTFLAG_BOOL_OK))
+		// Using number 0 or 1 for bool is OK.
+		return OK;
 	    if (give_msg)
 		arg_type_mismatch(expected, actual, argidx);
 	    return FAIL;