diff --git a/client/src/crypto/asn1dump.c b/client/src/crypto/asn1dump.c
index 025e200ca..32dc8f051 100644
--- a/client/src/crypto/asn1dump.c
+++ b/client/src/crypto/asn1dump.c
@@ -15,7 +15,7 @@
 //-----------------------------------------------------------------------------
 // asn.1 dumping
 //-----------------------------------------------------------------------------
-#define _POSIX_C_SOURCE 200809L                 // need for strnlen()
+
 #include "asn1dump.h"
 
 #include "commonutil.h"  // ARRAYLEN
@@ -344,17 +344,17 @@ static void asn1_tag_dump_object_id(const struct tlv *tlv, const struct asn1_tag
     } else {
         const char *ppstr = NULL;
         mbedtls_oid_get_attr_short_name(&asn1_buf, &ppstr);
-        if (ppstr && strnlen(ppstr, 1)) {
+        if (ppstr && str_nlen(ppstr, 1)) {
             PrintAndLogEx(NORMAL, " (%s)", ppstr);
             return;
         }
         mbedtls_oid_get_sig_alg_desc(&asn1_buf, &ppstr);
-        if (ppstr && strnlen(ppstr, 1)) {
+        if (ppstr && str_nlen(ppstr, 1)) {
             PrintAndLogEx(NORMAL, " (%s)", ppstr);
             return;
         }
         mbedtls_oid_get_extended_key_usage(&asn1_buf, &ppstr);
-        if (ppstr && strnlen(ppstr, 1)) {
+        if (ppstr && str_nlen(ppstr, 1)) {
             PrintAndLogEx(NORMAL, " (%s)", ppstr);
             return;
         }
diff --git a/client/src/mifare/desfirecore.c b/client/src/mifare/desfirecore.c
index 9c3326f83..077414c86 100644
--- a/client/src/mifare/desfirecore.c
+++ b/client/src/mifare/desfirecore.c
@@ -43,6 +43,7 @@
 #include "mifare/mad.h"
 #include "mifare/aiddesfire.h"
 
+
 const CLIParserOption DesfireAlgoOpts[] = {
     {T_DES,    "des"},
     {T_3DES,   "2tdea"},
@@ -1749,7 +1750,7 @@ int DesfireFillAppList(DesfireContext_t *dctx, PICCInfo_t *PICCInfo, AppListS ap
                 memcpy(
                     appList[indx].appDFName,
                     &buf[i * 24 + 1 + 5],
-                    // strnlen((char *)&buf[i * 24 + 1 + 5], 16)
+                    // str_nlen((char *)&buf[i * 24 + 1 + 5], 16)
                     16
                 );
             }
@@ -2879,7 +2880,7 @@ int DesfireISOSelect(DesfireContext_t *dctx, DesfireISOSelectControl cntr, uint8
 }
 
 int DesfireISOSelectDF(DesfireContext_t *dctx, char *dfname, uint8_t *resp, size_t *resplen) {
-    return DesfireISOSelect(dctx, ISSDFName, (uint8_t *)dfname, strnlen(dfname, 16), resp, resplen);
+    return DesfireISOSelect(dctx, ISSDFName, (uint8_t *)dfname, str_nlen(dfname, 16), resp, resplen);
 }
 
 int DesfireISOGetChallenge(DesfireContext_t *dctx, DesfireCryptoAlgorithm keytype, uint8_t *resp, size_t *resplen) {
diff --git a/client/src/util.c b/client/src/util.c
index 640178959..79d3c312b 100644
--- a/client/src/util.c
+++ b/client/src/util.c
@@ -1198,6 +1198,16 @@ char *str_ndup(const char *src, size_t len) {
     return dest;
 }
 
+size_t str_nlen(const char *src, size_t maxlen) {
+    size_t len = 0;
+    if(src {
+        for(char c = *src; (len < maxlen && c != '\0'); c = *++src) {
+            len++;
+        }
+    }
+    return len;
+}
+
 /**
  * Converts a hex string to component "hi2", "hi" and "lo" 32-bit integers
  * one nibble at a time.
diff --git a/client/src/util.h b/client/src/util.h
index 3b9a70183..1d6df987d 100644
--- a/client/src/util.h
+++ b/client/src/util.h
@@ -147,6 +147,7 @@ void strcleanrn(char *buf, size_t len);
 void strcreplace(char *buf, size_t len, char from, char to);
 char *str_dup(const char *src);
 char *str_ndup(const char *src, size_t len);
+size_t str_nlen(const char *src, size_t maxlen);
 int hexstring_to_u96(uint32_t *hi2, uint32_t *hi, uint32_t *lo, const char *str);
 int binstring_to_u96(uint32_t *hi2, uint32_t *hi, uint32_t *lo, const char *str);
 int binarray_to_u96(uint32_t *hi2, uint32_t *hi, uint32_t *lo, const uint8_t *arr, int arrlen);