diff --git a/CMakeLists.txt b/CMakeLists.txt
index 15be22bf..da1460d0 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -58,7 +58,7 @@ set(CMAKE_MACOSX_RPATH TRUE)
 # micro version is changed with a set of small changes or bugfixes anywhere in the project.
 set(LIBNETCONF2_MAJOR_VERSION 4)
 set(LIBNETCONF2_MINOR_VERSION 2)
-set(LIBNETCONF2_MICRO_VERSION 14)
+set(LIBNETCONF2_MICRO_VERSION 15)
 set(LIBNETCONF2_VERSION ${LIBNETCONF2_MAJOR_VERSION}.${LIBNETCONF2_MINOR_VERSION}.${LIBNETCONF2_MICRO_VERSION})
 
 # Version of the library
@@ -66,7 +66,7 @@ set(LIBNETCONF2_VERSION ${LIBNETCONF2_MAJOR_VERSION}.${LIBNETCONF2_MINOR_VERSION
 # with backward compatible change and micro version is connected with any internal change of the library.
 set(LIBNETCONF2_MAJOR_SOVERSION 5)
 set(LIBNETCONF2_MINOR_SOVERSION 3)
-set(LIBNETCONF2_MICRO_SOVERSION 3)
+set(LIBNETCONF2_MICRO_SOVERSION 4)
 set(LIBNETCONF2_SOVERSION_FULL ${LIBNETCONF2_MAJOR_SOVERSION}.${LIBNETCONF2_MINOR_SOVERSION}.${LIBNETCONF2_MICRO_SOVERSION})
 set(LIBNETCONF2_SOVERSION ${LIBNETCONF2_MAJOR_SOVERSION})
 
diff --git a/src/session_openssl.c b/src/session_openssl.c
index 2b4a0842..6484a526 100644
--- a/src/session_openssl.c
+++ b/src/session_openssl.c
@@ -1035,10 +1035,17 @@ nc_tls_get_err_reasons(void)
     unsigned int e;
     int reason_size, reason_len;
     char *reasons = NULL;
+    const char *err_reason;
 
     reason_size = 1;
     reason_len = 0;
     while ((e = ERR_get_error())) {
+        err_reason = ERR_reason_error_string(e);
+        if (!err_reason) {
+            /* couldn't map value to anything from https://datatracker.ietf.org/doc/html/rfc8446#appendix-B.2 */
+            DBG(NULL, "Unknown OpenSSL error (err code %u).", e);
+            err_reason = "unknown AlertDescription value";
+        }
         if (reason_len) {
             /* add "; " */
             reason_size += 2;
@@ -1046,10 +1053,10 @@ nc_tls_get_err_reasons(void)
             NC_CHECK_ERRMEM_RET(!reasons, NULL);
             reason_len += sprintf(reasons + reason_len, "; ");
         }
-        reason_size += strlen(ERR_reason_error_string(e));
+        reason_size += strlen(err_reason);
         reasons = nc_realloc(reasons, reason_size);
         NC_CHECK_ERRMEM_RET(!reasons, NULL);
-        reason_len += sprintf(reasons + reason_len, "%s", ERR_reason_error_string(e));
+        reason_len += sprintf(reasons + reason_len, "%s", err_reason);
     }
 
     return reasons;