diff --git a/src/emucore/OSystem.cxx b/src/emucore/OSystem.cxx
index 0dff979b4..2e34e4ded 100644
--- a/src/emucore/OSystem.cxx
+++ b/src/emucore/OSystem.cxx
@@ -22,8 +22,8 @@
 #include <fstream>
 #include <zlib.h>
 
+#include <ctime>
 #ifdef HAVE_GETTIMEOFDAY
-  #include <time.h>
   #include <sys/time.h>
 #endif
 
@@ -95,6 +95,9 @@ OSystem::OSystem()
     myFont(NULL),
     myConsoleFont(NULL)
 {
+  // Calculate startup time
+  myMillisAtStart = (uInt32)(time(NULL) * 1000);
+
   // Get built-in features
   #ifdef DISPLAY_OPENGL
     myFeatures += "OpenGL ";
@@ -918,12 +921,17 @@ void OSystem::stateChanged(EventHandler::State state)
 uInt64 OSystem::getTicks() const
 {
 #ifdef HAVE_GETTIMEOFDAY
+  // Gettimeofday natively refers to the UNIX epoch (a set time in the past)
   timeval now;
   gettimeofday(&now, 0);
 
   return uInt64(now.tv_sec) * 1000000 + now.tv_usec;
 #else
-  return uInt64(SDL_GetTicks()) * 1000;
+  // We use SDL_GetTicks, but add in the time when the application was
+  // initialized.  This is necessary, since SDL_GetTicks only measures how
+  // long SDL has been running, which can be the same between multiple runs
+  // of the application.
+  return uInt64(SDL_GetTicks() + myMillisAtStart) * 1000;
 #endif
 }
 
diff --git a/src/emucore/OSystem.hxx b/src/emucore/OSystem.hxx
index f8d3e23ea..f242daea5 100644
--- a/src/emucore/OSystem.hxx
+++ b/src/emucore/OSystem.hxx
@@ -377,20 +377,21 @@ class OSystem
 
   public:
     //////////////////////////////////////////////////////////////////////
-    // The following methods are system-specific and must be implemented
-    // in derived classes.
+    // The following methods are system-specific and can be overrided in
+    // derived classes.  Otherwise, the base methods will be used.
     //////////////////////////////////////////////////////////////////////
     /**
-      This method returns number of ticks in microseconds.
+      This method returns number of ticks in microseconds since some
+      pre-defined time in the past.  *NOTE*: it is necessary that this
+      pre-defined time exists between runs of the application, and must
+      be (relatively) unique.  For example, the time since the system
+      started running is not a good choice, since it can be duplicated.
+      The current implementation uses time since the UNIX epoch.
 
       @return Current time in microseconds.
     */
     virtual uInt64 getTicks() const;
 
-    //////////////////////////////////////////////////////////////////////
-    // The following methods are system-specific and can be overrided in
-    // derived classes.  Otherwise, the base methods will be used.
-    //////////////////////////////////////////////////////////////////////
     /**
       This method runs the main loop.  Since different platforms
       may use different timing methods and/or algorithms, this method can
@@ -503,6 +504,9 @@ class OSystem
     // Time per frame for a video update, based on the current framerate
     uInt32 myTimePerFrame;
 
+    // The time (in milliseconds) from the UNIX epoch when the application starts
+    uInt32 myMillisAtStart;
+
     // Indicates whether to stop the main loop
     bool myQuitLoop;