diff --git a/lib/Driver/HostInfo.cpp b/lib/Driver/HostInfo.cpp
index 5f2460f..39a688a 100644
--- a/lib/Driver/HostInfo.cpp
+++ b/lib/Driver/HostInfo.cpp
@@ -11,6 +11,8 @@
 
 #include "clang/Driver/Arg.h"
 #include "clang/Driver/ArgList.h"
+#include "clang/Driver/Driver.h"
+#include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Option.h"
 #include "clang/Driver/Options.h"
 
@@ -59,6 +61,37 @@
                                   const char *ArchName) const;
 };
 
+/// GetReleaseVersion - Parse (([0-9]+)(.([0-9]+)(.([0-9]+)?))?)? and
+/// return the grouped values as integers. Numbers which are not
+/// provided are set to 0.
+///
+/// \return True if the entire string was parsed (9.2), or all groups
+/// were parsed (10.3.5extrastuff).
+static bool GetReleaseVersion(const char *Str, unsigned &Major, 
+                              unsigned &Minor, unsigned &Micro) {
+  Major = Minor = Micro = 0;
+  if (*Str == '\0') 
+    return true;
+
+  char *End;
+  Major = (unsigned) strtol(Str, &End, 10);
+  if (*Str != '\0' && *End == '\0')
+    return true;
+  if (*End != '.')
+    return false;
+  
+  Str = End+1;
+  Minor = (unsigned) strtol(Str, &End, 10);
+  if (*Str != '\0' && *End == '\0')
+    return true;
+  if (*End != '.')
+    return false;
+
+  Str = End+1;
+  Micro = (unsigned) strtol(Str, &End, 10);
+  return true;
+}
+
 DarwinHostInfo::DarwinHostInfo(const Driver &D, const char *_Arch, 
                                const char *_Platform, const char *_OS) 
   : HostInfo(D, _Arch, _Platform, _OS) {
@@ -67,7 +100,14 @@
           getArchName() == "ppc" || getArchName() == "ppc64") &&
          "Unknown Darwin arch.");
 
-  // FIXME: How to deal with errors?
+  assert(memcmp(&getOSName()[0], "darwin", 6) == 0 &&
+         "Unknown Darwin platform.");
+  const char *Release = &getOSName()[6];
+  if (!GetReleaseVersion(Release, DarwinVersion[0], DarwinVersion[1], 
+                         DarwinVersion[2])) {
+    D.Diag(clang::diag::err_drv_invalid_darwin_version)
+      << Release;
+  }
   
   // We can only call 4.2.1 for now.
   GCCVersion[0] = 4;