diff --git a/crypto/bn_extra/convert.c b/crypto/bn_extra/convert.c
index 6e930fc69..e31de1f06 100644
--- a/crypto/bn_extra/convert.c
+++ b/crypto/bn_extra/convert.c
@@ -310,7 +310,7 @@ err:
 }
 
 int BN_dec2bn(BIGNUM **outp, const char *in) {
-  return bn_x2bn(outp, in, decode_dec, isdigit);
+  return bn_x2bn(outp, in, decode_dec, OPENSSL_isdigit);
 }
 
 int BN_asc2bn(BIGNUM **outp, const char *in) {
diff --git a/crypto/bytestring/cbs.c b/crypto/bytestring/cbs.c
index efafbfb44..30e38fad1 100644
--- a/crypto/bytestring/cbs.c
+++ b/crypto/bytestring/cbs.c
@@ -232,7 +232,7 @@ int CBS_get_u64_decimal(CBS *cbs, uint64_t *out) {
   int seen_digit = 0;
   while (CBS_len(cbs) != 0) {
     uint8_t c = CBS_data(cbs)[0];
-    if (!isdigit(c)) {
+    if (!OPENSSL_isdigit(c)) {
       break;
     }
     CBS_skip(cbs, 1);
@@ -753,13 +753,13 @@ static int cbs_get_two_digits(CBS *cbs, int *out) {
   if (!CBS_get_u8(cbs, &first_digit)) {
     return 0;
   }
-  if (!isdigit(first_digit)) {
+  if (!OPENSSL_isdigit(first_digit)) {
     return 0;
   }
   if (!CBS_get_u8(cbs, &second_digit)) {
     return 0;
   }
-  if (!isdigit(second_digit)) {
+  if (!OPENSSL_isdigit(second_digit)) {
     return 0;
   }
   *out = (first_digit - '0') * 10 + (second_digit - '0');
diff --git a/crypto/mem.c b/crypto/mem.c
index e9d3d728f..9dedab965 100644
--- a/crypto/mem.c
+++ b/crypto/mem.c
@@ -308,6 +308,10 @@ char *OPENSSL_strdup(const char *s) {
   return ret;
 }
 
+int OPENSSL_isdigit(int c) {
+  return c >= '0' && c <= '9';
+}
+
 int OPENSSL_tolower(int c) {
   if (c >= 'A' && c <= 'Z') {
     return c + ('a' - 'A');
diff --git a/include/openssl/mem.h b/include/openssl/mem.h
index 621604063..0fd1209fb 100644
--- a/include/openssl/mem.h
+++ b/include/openssl/mem.h
@@ -110,6 +110,10 @@ OPENSSL_EXPORT char *OPENSSL_strdup(const char *s);
 // OPENSSL_strnlen has the same behaviour as strnlen(3).
 OPENSSL_EXPORT size_t OPENSSL_strnlen(const char *s, size_t len);
 
+// OPENSSL_isdigit is a locale-independent version of isdigit(3), It
+// only recognizes '0' through '9' as digits.
+OPENSSL_EXPORT int OPENSSL_isdigit(int c);
+
 // OPENSSL_tolower is a locale-independent version of tolower(3). It only
 // lowercases ASCII values. Other values are returned as-is.
 OPENSSL_EXPORT int OPENSSL_tolower(int c);
diff --git a/ssl/test/test_config.cc b/ssl/test/test_config.cc
index 850cb23fb..5764b63c5 100644
--- a/ssl/test/test_config.cc
+++ b/ssl/test/test_config.cc
@@ -63,7 +63,7 @@ bool StringToInt(T *out, const char *str) {
 
   // |strtoull| allows leading '-' with wraparound. Additionally, both
   // functions accept empty strings and leading whitespace.
-  if (!isdigit(static_cast<unsigned char>(*str)) &&
+  if (!OPENSSL_isdigit(static_cast<unsigned char>(*str)) &&
       (!std::is_signed<T>::value || *str != '-')) {
     return false;
   }