diff --git a/include/mbedtls/asn1.h b/include/mbedtls/asn1.h
index 96c1c9a..2fb6de0 100644
--- a/include/mbedtls/asn1.h
+++ b/include/mbedtls/asn1.h
@@ -89,6 +89,18 @@
 #define MBEDTLS_ASN1_CONSTRUCTED             0x20
 #define MBEDTLS_ASN1_CONTEXT_SPECIFIC        0x80
 
+/* Slightly smaller way to check if tag is a string tag
+ * compared to canonical implementation. */
+#define MBEDTLS_ASN1_IS_STRING_TAG( tag )                                     \
+    ( ( tag ) < 32u && (                                                      \
+        ( ( 1u << ( tag ) ) & ( ( 1u << MBEDTLS_ASN1_BMP_STRING )       |     \
+                                ( 1u << MBEDTLS_ASN1_UTF8_STRING )      |     \
+                                ( 1u << MBEDTLS_ASN1_T61_STRING )       |     \
+                                ( 1u << MBEDTLS_ASN1_IA5_STRING )       |     \
+                                ( 1u << MBEDTLS_ASN1_UNIVERSAL_STRING ) |     \
+                                ( 1u << MBEDTLS_ASN1_PRINTABLE_STRING ) |     \
+                                ( 1u << MBEDTLS_ASN1_BIT_STRING ) ) ) != 0 ) )
+
 /*
  * Bit masks for each of the components of an ASN.1 tag as specified in
  * ITU X.690 (08/2015), section 8.1 "General rules for encoding",
diff --git a/library/x509.c b/library/x509.c
index 2e7bd57..9d9db23 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -375,12 +375,11 @@
         return( MBEDTLS_ERR_X509_INVALID_NAME +
                 MBEDTLS_ERR_ASN1_OUT_OF_DATA );
 
-    if( **p != MBEDTLS_ASN1_BMP_STRING && **p != MBEDTLS_ASN1_UTF8_STRING      &&
-        **p != MBEDTLS_ASN1_T61_STRING && **p != MBEDTLS_ASN1_PRINTABLE_STRING &&
-        **p != MBEDTLS_ASN1_IA5_STRING && **p != MBEDTLS_ASN1_UNIVERSAL_STRING &&
-        **p != MBEDTLS_ASN1_BIT_STRING )
+    if( !MBEDTLS_ASN1_IS_STRING_TAG( **p ) )
+    {
         return( MBEDTLS_ERR_X509_INVALID_NAME +
                 MBEDTLS_ERR_ASN1_UNEXPECTED_TAG );
+    }
 
     val = &cur->val;
     val->tag = *(*p)++;