diff --git a/checkin_notes b/checkin_notes
index b5bc1e2705..b0d0c328e2 100755
--- a/checkin_notes
+++ b/checkin_notes
@@ -14229,3 +14229,12 @@ David  27 June 2004
         hostinfo_unix.C
     lib/
         app_ipc.h
+
+Rom    27 June 2004
+    - Prevent the reuse of shared memory segments with ones that are already
+      in use on Windows.
+
+    client/
+        app.C
+    lib/
+        shmem.C
diff --git a/client/app.C b/client/app.C
index f9b0c7df7e..f2095037b7 100644
--- a/client/app.C
+++ b/client/app.C
@@ -243,7 +243,23 @@ int ACTIVE_TASK::write_app_init_file(APP_INIT_DATA& aid) {
     // make a unique key for core/app shared memory segment
     //
 #ifdef _WIN32
-    sprintf(aid.comm_obj_name, "boinc_%d", slot);
+    int     i = 0;
+    char    szSharedMemoryName[256];
+    HANDLE  hSharedMemoryHandle;
+
+    do {
+        memset(szSharedMemoryName, '\0', sizeof(szSharedMemoryName));
+        sprintf(szSharedMemoryName, "boinc_%d", slot);
+        i++;
+    } while((!(hSharedMemoryHandle = create_shmem(szSharedMemoryName, 1024, NULL))) || (1024 < i));
+
+    if (hSharedMemoryHandle)
+        CloseHandle(hSharedMemoryHandle);
+
+    if (1024 < i)
+        return ERR_SEMOP;
+
+    strcpy(aid.comm_obj_name, szSharedMemoryName);
 #elif HAVE_SYS_IPC_H
     aid.shm_key = ftok(init_data_path, slot);
 #else
diff --git a/lib/shmem.C b/lib/shmem.C
index bba11c923d..8d078c268f 100755
--- a/lib/shmem.C
+++ b/lib/shmem.C
@@ -57,6 +57,7 @@ HANDLE create_shmem(LPCTSTR seg_name, int size, void** pp) {
     hSharedMem = CreateFileMapping(INVALID_HANDLE_VALUE, &security,
         PAGE_READWRITE, 0, size, seg_name);
     if (!hSharedMem) return NULL;
+    if (hSharedMem && (ERROR_ALREADY_EXISTS == GetLastError())) return NULL; 
 
     pMemPtr = MapViewOfFile( hSharedMem, FILE_MAP_ALL_ACCESS, 0, 0, 0 );
     *pp = pMemPtr;