diff --git a/Source/cmIfCommand.h b/Source/cmIfCommand.h
index 4893a17b6..0a1fe06f3 100644
--- a/Source/cmIfCommand.h
+++ b/Source/cmIfCommand.h
@@ -149,7 +149,12 @@ public:
       "  if(file1 IS_NEWER_THAN file2)\n"
       "True if file1 is newer than file2 or if one of the two files "
       "doesn't exist. "
-      "Behavior is well-defined only for full paths.\n"
+      "Behavior is well-defined only for full paths. "
+      "If the file time stamps are exactly the same, an "
+      "IS_NEWER_THAN comparison returns true, so that any dependent "
+      "build operations will occur in the event of a tie. "
+      "This includes the case of passing the same file name for both "
+      "file1 and file2.\n"
       "  if(IS_DIRECTORY directory-name)\n"
       "True if the given name is a directory.  "
       "Behavior is well-defined only for full paths.\n"