diff --git a/apps/dsm/mods/mod_zrtp/ModZrtp.cpp b/apps/dsm/mods/mod_zrtp/ModZrtp.cpp
index d09026f5..f104a949 100644
--- a/apps/dsm/mods/mod_zrtp/ModZrtp.cpp
+++ b/apps/dsm/mods/mod_zrtp/ModZrtp.cpp
@@ -182,7 +182,7 @@ EXEC_ACTION_START(ZRTPGetSessionInfoAction) {
 bool hex2zid(const string& zid1, char* buffer) {
   for (size_t i=0;i<zid1.length()/2;i++) {
     unsigned int h;
-    if (reverse_hex2int(zid1.substr(i*2, 2), h)) {
+    if (!reverse_hex2int(zid1.substr(i*2, 2), h)) {
       ERROR("in zid: '%s' is no hex number\n", zid1.substr(i*2, 2).c_str());
       return false;
     }
diff --git a/apps/sbc/SBCCallProfile.cpp b/apps/sbc/SBCCallProfile.cpp
index 5f6db0ac..3885bcb6 100644
--- a/apps/sbc/SBCCallProfile.cpp
+++ b/apps/sbc/SBCCallProfile.cpp
@@ -821,7 +821,7 @@ bool SBCCallProfile::evaluate(ParamReplacerCtx& ctx,
     if (msgflags_symmetric_rtp) {
       string str_msg_flags = getHeader(req.hdrs,"P-MsgFlags", true);
       unsigned int msg_flags = 0;
-      if(reverse_hex2int(str_msg_flags,msg_flags)){
+      if(!reverse_hex2int(str_msg_flags,msg_flags)){
         ERROR("while parsing 'P-MsgFlags' header\n");
         msg_flags = 0;
       }
diff --git a/apps/sbc/arg_conversion.cpp b/apps/sbc/arg_conversion.cpp
index b05468a0..2c75d31a 100644
--- a/apps/sbc/arg_conversion.cpp
+++ b/apps/sbc/arg_conversion.cpp
@@ -157,7 +157,7 @@ bool username2arg(const string &src, AmArg &dst)
   while (pos != string::npos) {
     if (pos + 2 >= encoded.size()) return false;
     unsigned int c;
-    if (reverse_hex2int(string() + encoded[pos + 2] + encoded[pos + 1], c)) {
+    if (!reverse_hex2int(string() + encoded[pos + 2] + encoded[pos + 1], c)) {
       DBG("%c%c does not convert from hex\n", encoded[pos + 1], encoded[pos + 2]);
       return false;
     }
diff --git a/core/AmUtils.cpp b/core/AmUtils.cpp
index 1297e17b..e932e2b9 100644
--- a/core/AmUtils.cpp
+++ b/core/AmUtils.cpp
@@ -188,7 +188,7 @@ string double2str(double val) {
  * Convert a reversed hex string to uint.
  * @param str    [in]  string to convert.
  * @param result [out] result integer.
- * @return true if failed. 
+ * @return true on success
  */
 bool reverse_hex2int(const string& str, unsigned int& result)
 {
diff --git a/core/AmZRTP.cpp b/core/AmZRTP.cpp
index 7c4e0298..9bd02fcc 100644
--- a/core/AmZRTP.cpp
+++ b/core/AmZRTP.cpp
@@ -81,7 +81,7 @@ int AmZRTP::init() {
 
     for (size_t i=0;i<sizeof(zrtp_instance_zid);i++) {
       unsigned int h;
-      if (reverse_hex2int(zid_hex.substr(i*2, 2), h)) {
+      if (!reverse_hex2int(zid_hex.substr(i*2, 2), h)) {
 	ERROR("in zid_hex in zrtp.conf: '%s' is no hex number\n", zid_hex.substr(i*2, 2).c_str());
 	return -1;
       }