diff --git a/py/objstr.c b/py/objstr.c
index 7d7f0e1dfa..321bb058dc 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -1163,7 +1163,7 @@ STATIC vstr_t mp_obj_str_format_helper(const char *str, const char *top, int *ar
                 s++;
             }
             if (*s == '0') {
-                if (!align) {
+                if (!align && arg_looks_numeric(arg)) {
                     align = '=';
                 }
                 if (!fill) {
diff --git a/tests/basics/string_format_cp310.py b/tests/basics/string_format_cp310.py
new file mode 100644
index 0000000000..77295330be
--- /dev/null
+++ b/tests/basics/string_format_cp310.py
@@ -0,0 +1,9 @@
+# Python 3.10+ functionality test for {} format string
+
+def test(fmt, *args):
+    print('{:8s}'.format(fmt) + '>' +  fmt.format(*args) + '<')
+
+test("{:0s}", "ab")
+test("{:06s}", "ab")
+test("{:<06s}", "ab")
+test("{:>06s}", "ab")
diff --git a/tests/basics/string_format_cp310.py.exp b/tests/basics/string_format_cp310.py.exp
new file mode 100644
index 0000000000..1c26473d83
--- /dev/null
+++ b/tests/basics/string_format_cp310.py.exp
@@ -0,0 +1,4 @@
+{:0s}   >ab<
+{:06s}  >ab0000<
+{:<06s} >ab0000<
+{:>06s} >0000ab<
diff --git a/tests/basics/string_format_error.py b/tests/basics/string_format_error.py
index 708348d59f..74dc6c52ed 100644
--- a/tests/basics/string_format_error.py
+++ b/tests/basics/string_format_error.py
@@ -1,7 +1,7 @@
 # tests for errors in {} format string
 
 try:
-    '{0:0}'.format('zzz')
+    '{0:=}'.format('zzz')
 except (ValueError):
     print('ValueError')