diff --git a/lib/System/Unix/Program.inc b/lib/System/Unix/Program.inc
index 2f3616e73a1..7fdf3872dd9 100644
--- a/lib/System/Unix/Program.inc
+++ b/lib/System/Unix/Program.inc
@@ -32,6 +32,9 @@
 #endif
 #ifdef HAVE_POSIX_SPAWN
 #include <spawn.h>
+#if !defined(__APPLE__)
+  extern char **environ;
+#endif
 #endif
 
 namespace llvm {
@@ -199,6 +202,10 @@ Program::Execute(const Path &path, const char **args, const char **envp,
       }
     }
 
+#if !defined(__APPLE__)
+    if (!envp) envp = (const char**)environ;
+#endif
+
     pid_t PID;
     int Err = posix_spawn(&PID, path.c_str(), &FileActions,
                           /*attrp*/0, (char**)args, (char**)envp);