diff --git a/Source/cmFileTimeComparison.cxx b/Source/cmFileTimeComparison.cxx
index 66a177172..acd132166 100644
--- a/Source/cmFileTimeComparison.cxx
+++ b/Source/cmFileTimeComparison.cxx
@@ -38,6 +38,8 @@ public:
   // Internal comparison method.
   inline bool FileTimeCompare(const char* f1, const char* f2, int* result);
 
+  bool FileTimesDiffer(const char* f1, const char* f2);
+
 private:
 #if defined(CMAKE_BUILD_WITH_CMAKE)
   // Use a hash table to efficiently map from file name to modification time.
@@ -59,6 +61,8 @@ private:
   inline bool Stat(const char* fname, cmFileTimeComparison_Type* st);
   inline int Compare(cmFileTimeComparison_Type* st1,
                      cmFileTimeComparison_Type* st2);
+  inline bool TimesDiffer(cmFileTimeComparison_Type* st1,
+                          cmFileTimeComparison_Type* st2);
 };
 
 //----------------------------------------------------------------------------
@@ -123,6 +127,12 @@ bool cmFileTimeComparison::FileTimeCompare(const char* f1,
   return this->Internals->FileTimeCompare(f1, f2, result);
 }
 
+//----------------------------------------------------------------------------
+bool cmFileTimeComparison::FileTimesDiffer(const char* f1, const char* f2)
+{
+  return this->Internals->FileTimesDiffer(f1, f2);
+}
+
 //----------------------------------------------------------------------------
 int cmFileTimeComparisonInternal::Compare(cmFileTimeComparison_Type* s1, 
                                           cmFileTimeComparison_Type* s2)
@@ -165,6 +175,66 @@ int cmFileTimeComparisonInternal::Compare(cmFileTimeComparison_Type* s1,
 #endif
 }
 
+//----------------------------------------------------------------------------
+bool cmFileTimeComparisonInternal::TimesDiffer(cmFileTimeComparison_Type* s1,
+                                               cmFileTimeComparison_Type* s2)
+{
+#if !defined(_WIN32) || defined(__CYGWIN__)
+# if cmsys_STAT_HAS_ST_MTIM
+  // Times are integers in units of 1ns.
+  long long bil = 1000000000;
+  long long t1 = s1->st_mtim.tv_sec * bil + s1->st_mtim.tv_nsec;
+  long long t2 = s2->st_mtim.tv_sec * bil + s2->st_mtim.tv_nsec;
+  if(t1 < t2)
+    {
+    return (t2 - t1) >= bil;
+    }
+  else if(t2 < t1)
+    {
+    return (t1 - t2) >= bil;
+    }
+  else
+    {
+    return false;
+    }
+# else
+  // Times are integers in units of 1s.
+  if(s1->st_mtime < s2->st_mtime)
+    {
+    return (s2->st_mtime - s1->st_mtime) >= 1;
+    }
+  else if(s1->st_mtime > s2->st_mtime)
+    {
+    return (s1->st_mtime - s2->st_mtime) >= 1;
+    }
+  else
+    {
+    return false;
+    }
+# endif
+#else
+  // Times are integers in units of 100ns.
+  LARGE_INTEGER t1;
+  LARGE_INTEGER t2;
+  t1.LowPart = s1->dwLowDateTime;
+  t1.HighPart = s1->dwHighDateTime;
+  t2.LowPart = s2->dwLowDateTime;
+  t2.HighPart = s2->dwHighDateTime;
+  if(t1.QuadPart < t2.QuadPart)
+    {
+    return (t2.QuadPart - t1.QuadPart) >= static_cast<LONGLONG>(10000000);
+    }
+  else if(t2.QuadPart < t1.QuadPart)
+    {
+    return (t1.QuadPart - t2.QuadPart) >= static_cast<LONGLONG>(10000000);
+    }
+  else
+    {
+    return false;
+    }
+#endif
+}
+
 //----------------------------------------------------------------------------
 bool cmFileTimeComparisonInternal::FileTimeCompare(const char* f1,
                                                    const char* f2,
@@ -187,3 +257,23 @@ bool cmFileTimeComparisonInternal::FileTimeCompare(const char* f1,
     return false;
     }
 }
+
+//----------------------------------------------------------------------------
+bool cmFileTimeComparisonInternal::FileTimesDiffer(const char* f1,
+                                                   const char* f2)
+{
+  // Get the modification time for each file.
+  cmFileTimeComparison_Type s1;
+  cmFileTimeComparison_Type s2;
+  if(this->Stat(f1, &s1) &&
+     this->Stat(f2, &s2))
+    {
+    // Compare the two modification times.
+    return this->TimesDiffer(&s1, &s2);
+    }
+  else
+    {
+    // No comparison available.  Default to different times.
+    return true;
+    }
+}
diff --git a/Source/cmFileTimeComparison.h b/Source/cmFileTimeComparison.h
index 5da97db72..8067e1d51 100644
--- a/Source/cmFileTimeComparison.h
+++ b/Source/cmFileTimeComparison.h
@@ -40,6 +40,12 @@ public:
    */
   bool FileTimeCompare(const char* f1, const char* f2, int* result);
 
+  /**
+   *  Compare file modification times.  Return true unless both files
+   *  exist and have modification times less than 1 second apart.
+   */
+  bool FileTimesDiffer(const char* f1, const char* f2);
+
 protected:
   
   cmFileTimeComparisonInternal* Internals;