diff --git a/crypto/mem.c b/crypto/mem.c
index 390ca2e73..f451a12dc 100644
--- a/crypto/mem.c
+++ b/crypto/mem.c
@@ -159,27 +159,50 @@ size_t OPENSSL_strnlen(const char *s, size_t len) {
 
 char *OPENSSL_strdup(const char *s) { return _strdup(s); }
 
-int OPENSSL_strcasecmp(const char *a, const char *b) {
-  return _stricmp(a, b);
-}
-
-int OPENSSL_strncasecmp(const char *a, const char *b, size_t n) {
-  return _strnicmp(a, b, n);
-}
-
 #else
 
 char *OPENSSL_strdup(const char *s) { return strdup(s); }
 
+#endif
+
+int OPENSSL_tolower(int c) {
+  if (c >= 'A' && c <= 'Z') {
+    return c + ('a' - 'A');
+  }
+  return c;
+}
+
 int OPENSSL_strcasecmp(const char *a, const char *b) {
-  return strcasecmp(a, b);
+  for (size_t i = 0;; i++) {
+    const int aa = OPENSSL_tolower(a[i]);
+    const int bb = OPENSSL_tolower(b[i]);
+
+    if (aa < bb) {
+      return -1;
+    } else if (aa > bb) {
+      return 1;
+    } else if (aa == 0) {
+      return 0;
+    }
+  }
 }
 
 int OPENSSL_strncasecmp(const char *a, const char *b, size_t n) {
-  return strncasecmp(a, b, n);
-}
+  for (size_t i = 0; i < n; i++) {
+    const int aa = OPENSSL_tolower(a[i]);
+    const int bb = OPENSSL_tolower(b[i]);
 
-#endif
+    if (aa < bb) {
+      return -1;
+    } else if (aa > bb) {
+      return 1;
+    } else if (aa == 0) {
+      return 0;
+    }
+  }
+
+  return 0;
+}
 
 int BIO_snprintf(char *buf, size_t n, const char *format, ...) {
   va_list args;
diff --git a/crypto/x509/x_name.c b/crypto/x509/x_name.c
index e6eeb957c..5fa9077b0 100644
--- a/crypto/x509/x_name.c
+++ b/crypto/x509/x_name.c
@@ -492,7 +492,7 @@ static int asn1_string_canon(ASN1_STRING *out, ASN1_STRING *in)
             }
             while (!(*from & 0x80) && isspace(*from));
         } else {
-            *to++ = tolower(*from);
+            *to++ = OPENSSL_tolower(*from);
             from++;
             i++;
         }
diff --git a/crypto/x509v3/v3_utl.c b/crypto/x509v3/v3_utl.c
index fe7787bbe..feb3dc6aa 100644
--- a/crypto/x509v3/v3_utl.c
+++ b/crypto/x509v3/v3_utl.c
@@ -454,15 +454,13 @@ unsigned char *string_to_hex(const char *str, long *len)
             OPENSSL_free(hexbuf);
             return NULL;
         }
-        if (isupper(ch))
-            ch = tolower(ch);
-        if (isupper(cl))
-            cl = tolower(cl);
 
         if ((ch >= '0') && (ch <= '9'))
             ch -= '0';
         else if ((ch >= 'a') && (ch <= 'f'))
             ch -= 'a' - 10;
+        else if ((ch >= 'A') && (ch <= 'F'))
+            ch -= 'A' - 10;
         else
             goto badhex;
 
@@ -470,6 +468,8 @@ unsigned char *string_to_hex(const char *str, long *len)
             cl -= '0';
         else if ((cl >= 'a') && (cl <= 'f'))
             cl -= 'a' - 10;
+        else if ((cl >= 'A') && (cl <= 'F'))
+            cl -= 'A' - 10;
         else
             goto badhex;
 
diff --git a/include/openssl/mem.h b/include/openssl/mem.h
index 5d96a2d72..c43a16a07 100644
--- a/include/openssl/mem.h
+++ b/include/openssl/mem.h
@@ -104,10 +104,13 @@ 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_strcasecmp has the same behaviour as strcasecmp(3). */
+/* OPENSSL_tolower is a locale-independent version of tolower(3). */
+OPENSSL_EXPORT int OPENSSL_tolower(int c);
+
+/* OPENSSL_strcasecmp is a locale-independent version of strcasecmp(3). */
 OPENSSL_EXPORT int OPENSSL_strcasecmp(const char *a, const char *b);
 
-/* OPENSSL_strncasecmp has the same behaviour as strncasecmp(3). */
+/* OPENSSL_strncasecmp is a locale-independent version of strncasecmp(3). */
 OPENSSL_EXPORT int OPENSSL_strncasecmp(const char *a, const char *b, size_t n);
 
 /* DECIMAL_SIZE returns an upper bound for the length of the decimal