1 files changed, 8 insertions, 6 deletions
diff --git a/lib/System/Unix/Unix.h b/lib/System/Unix/Unix.h
index 2f57b68c8e..741a817f45 100644
--- a/lib/System/Unix/Unix.h
+++ b/lib/System/Unix/Unix.h
@@ -66,24 +66,26 @@
 # define WIFEXITED(stat_val) (((stat_val) & 255) == 0)
 #endif
 
-inline void ThrowErrno(const std::string& prefix) {
+inline void ThrowErrno(const std::string& prefix, int errnum = -1) {
     char buffer[MAXPATHLEN];
     buffer[0] = 0;
+    if (errnum == -1)
+      errnum = errno;
 #ifdef HAVE_STRERROR_R
     // strerror_r is thread-safe.
-    if (errno)
-      strerror_r(errno,buffer,MAXPATHLEN-1);
+    if (errnum)
+      strerror_r(errnum,buffer,MAXPATHLEN-1);
 #elif HAVE_STRERROR
     // Copy the thread un-safe result of strerror into
     // the buffer as fast as possible to minimize impact
     // of collision of strerror in multiple threads.
-    if (errno)
-      strncpy(buffer,strerror(errno),MAXPATHLEN-1);
+    if (errnum)
+      strncpy(buffer,strerror(errnum),MAXPATHLEN-1);
     buffer[MAXPATHLEN-1] = 0;
 #else
     // Strange that this system doesn't even have strerror
     // but, oh well, just use a generic message
-    sprintf(buffer, "Error #%d", errno);
+    sprintf(buffer, "Error #%d", errnum);
 #endif
     throw prefix + ": " + buffer;
 }