diff --git a/include/common.h b/include/common.h
index 680ddbe6c..806cd740a 100644
--- a/include/common.h
+++ b/include/common.h
@@ -28,6 +28,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <search.h>
+#include <fcntl.h>
 
 #ifdef _POSIX
 #include <sys/time.h>
@@ -62,7 +63,6 @@ typedef void *HM_LIB;
 #include <tchar.h>
 #include <psapi.h>
 #include <io.h>
-#include <fcntl.h>
 
 typedef UINT8  uint8_t;
 typedef UINT16 uint16_t;
diff --git a/include/shared.h b/include/shared.h
index 259e93bdd..d1362f976 100644
--- a/include/shared.h
+++ b/include/shared.h
@@ -1832,6 +1832,14 @@ char *logfile_generate_topid ();
 char *logfile_generate_subid ();
 void logfile_append (const char *fmt, ...);
 
+#if F_SETLKW
+void lock_file (FILE *fp);
+void unlock_file (FILE *fp);
+#else
+#define lock_file(dummy) {}
+#define unlock_file(dummy) {}
+#endif
+
 #ifdef _WIN
 void fsync (int fd);
 #endif
diff --git a/src/oclHashcat.c b/src/oclHashcat.c
index 6c53b56af..ea5ef21ed 100644
--- a/src/oclHashcat.c
+++ b/src/oclHashcat.c
@@ -2081,6 +2081,8 @@ static void check_hash (hc_device_param_t *device_param, const uint salt_pos, co
 
   if (pot_fp)
   {
+    lock_file (pot_fp);
+
     fprintf (pot_fp, "%s:", out_buf);
 
     format_plain (pot_fp, plain_ptr, plain_len, 1);
@@ -2088,6 +2090,8 @@ static void check_hash (hc_device_param_t *device_param, const uint salt_pos, co
     fputc ('\n', pot_fp);
 
     fflush (pot_fp);
+
+    unlock_file (pot_fp);
   }
 
   // outfile
@@ -2102,6 +2106,7 @@ static void check_hash (hc_device_param_t *device_param, const uint salt_pos, co
 
       out_fp = stdout;
     }
+    lock_file (out_fp);
   }
   else
   {
@@ -2141,6 +2146,8 @@ static void check_hash (hc_device_param_t *device_param, const uint salt_pos, co
 
     if ((fb_fp = fopen (loopback_file, "ab")) != NULL)
     {
+      lock_file (fb_fp);
+
       format_plain (fb_fp, plain_ptr, plain_len, 1);
 
       fputc ('\n', fb_fp);
@@ -16179,6 +16186,8 @@ int main (int argc, char **argv)
 
           if (dictstat_fp)
           {
+            lock_file (dictstat_fp);
+
             fwrite (dictstat_base, sizeof (dictstat_t), dictstat_nmemb, dictstat_fp);
 
             fclose (dictstat_fp);
diff --git a/src/shared.c b/src/shared.c
index 7d12036ed..7058b64b9 100644
--- a/src/shared.c
+++ b/src/shared.c
@@ -2627,6 +2627,32 @@ char *logfile_generate_subid ()
  * system
  */
 
+#if F_SETLKW
+void lock_file (FILE *fp)
+{
+  struct flock lock = { 0 };
+
+  lock.l_type = F_WRLCK;
+  while (fcntl(fileno(fp), F_SETLKW, &lock))
+  {
+    if (errno != EINTR)
+    {
+      log_error ("ERROR: failed acquiring write lock: %s", strerror (errno));
+
+      exit (-1);
+    }
+  }
+}
+
+void unlock_file (FILE *fp)
+{
+  struct flock lock = { 0 };
+
+  lock.l_type = F_UNLCK;
+  fcntl(fileno(fp), F_SETLK, &lock);
+}
+#endif /* F_SETLKW */
+
 #ifdef _WIN
 void fsync (int fd)
 {
@@ -4733,6 +4759,8 @@ void format_debug (char *debug_file, uint debug_mode, unsigned char *orig_plain_
   if (debug_file != NULL)
   {
     debug_fp = fopen (debug_file, "ab");
+
+    lock_file (debug_fp);
   }
   else
   {
@@ -8676,6 +8704,7 @@ void writeProgramBin (char *dst, u8 *binary, size_t binary_size)
   {
     FILE *fp = fopen (dst, "wb");
 
+    lock_file (fp);
     fwrite (binary, sizeof (u8), binary_size, fp);
 
     fflush (fp);