Index: lib/Driver/ToolChains.cpp
===================================================================
--- lib/Driver/ToolChains.cpp
+++ lib/Driver/ToolChains.cpp
@@ -1298,6 +1298,8 @@
   if (First.first.getAsInteger(10, GoodVersion.Major) || GoodVersion.Major < 0)
     return BadVersion;
   GoodVersion.MajorStr = First.first.str();
+  if (First.second.empty())
+    return GoodVersion;
   if (Second.first.getAsInteger(10, GoodVersion.Minor) || GoodVersion.Minor < 0)
     return BadVersion;
   GoodVersion.MinorStr = Second.first.str();
@@ -1305,6 +1307,7 @@
   // First look for a number prefix and parse that if present. Otherwise just
   // stash the entire patch string in the suffix, and leave the number
   // unspecified. This covers versions strings such as:
+  //   5        (handled above)
   //   4.4
   //   4.4.0
   //   4.4.x
Index: test/Driver/linux-ld.c
===================================================================
--- test/Driver/linux-ld.c
+++ test/Driver/linux-ld.c
@@ -388,6 +388,15 @@
 // CHECK-GCC-VERSION4: "{{.*}}ld{{(.exe)?}}" "--sysroot=[[SYSROOT:[^"]+]]"
 // CHECK-GCC-VERSION4: "{{.*}}/Inputs/gcc_version_parsing4/bin/../lib/gcc/i386-unknown-linux/4.7.99{{/|\\\\}}crtbegin.o"
 // CHECK-GCC-VERSION4: "-L{{.*}}/Inputs/gcc_version_parsing4/bin/../lib/gcc/i386-unknown-linux/4.7.99"
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     --target=i386-unknown-linux -m32 \
+// RUN:     -ccc-install-dir %S/Inputs/gcc_version_parsing5/bin \
+// RUN:     --gcc-toolchain="" \
+// RUN:     --sysroot=%S/Inputs/basic_linux_tree \
+// RUN:   | FileCheck --check-prefix=CHECK-GCC-VERSION5 %s
+// CHECK-GCC-VERSION5: "{{.*}}ld{{(.exe)?}}" "--sysroot=[[SYSROOT:[^"]+]]"
+// CHECK-GCC-VERSION5: "{{.*}}/Inputs/gcc_version_parsing5/bin/../lib/gcc/i386-unknown-linux/5{{/|\\\\}}crtbegin.o"
+// CHECK-GCC-VERSION5: "-L{{.*}}/Inputs/gcc_version_parsing5/bin/../lib/gcc/i386-unknown-linux/5"
 //
 // Test a simulated installation of libc++ on Linux, both through sysroot and
 // the installation path of Clang.