diff --git a/src/zm_ffmpeg.cpp b/src/zm_ffmpeg.cpp
index a0131d75f..6ff053c34 100644
--- a/src/zm_ffmpeg.cpp
+++ b/src/zm_ffmpeg.cpp
@@ -64,11 +64,15 @@ void log_libav_callback(void *ptr, int level, const char *fmt, va_list vargs) {
 
   if ( log ) {
     char logString[8192];
-    vsnprintf(logString, sizeof(logString)-1, fmt, vargs);
-    int length = strlen(logString);
-    // ffmpeg logs have a carriage return, so replace it with terminator
-    logString[length-1] = 0;
-    log->logPrint(false, __FILE__, __LINE__, log_level, logString);
+    int length = vsnprintf(logString, sizeof(logString)-1, fmt, vargs);
+    if ( length > 0 ) {
+      if ( static_cast<size_t>(length) > sizeof(logString)-1 ) length = sizeof(logString)-1;
+      // ffmpeg logs have a carriage return, so replace it with terminator
+      logString[length-1] = 0;
+      log->logPrint(false, __FILE__, __LINE__, log_level, logString);
+    } else {
+      log->logPrint(false, __FILE__, __LINE__, AV_LOG_ERROR, "Can't encode log from av. fmt was %s", fmt);
+    }
   }
 }