diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7388f2d0e82..b6fc32bb097 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -404,7 +404,7 @@ endif (EXISTS "${PROJECT_SOURCE_DIR}/.svn")
 # N.B.: if VERSION_NUMBER's major number is incremented without also
 # incrementing OLDEST_COMPATIBLE_VERSION we'll need to add another
 # symlink loop in core/CMakeLists.txt
-set(VERSION_NUMBER_DEFAULT "4.0.${VERSION_NUMBER_PATCHLEVEL}")
+set(VERSION_NUMBER_DEFAULT "4.1.${VERSION_NUMBER_PATCHLEVEL}")
 # do not store the default VERSION_NUMBER in the cache to prevent a stale one
 # from preventing future version updates in a pre-existing build dir
 set(VERSION_NUMBER "" CACHE STRING "Version number: leave empty for default")
@@ -942,8 +942,9 @@ string(REGEX REPLACE
   "^[0-9]+\\.([0-9]+)\\..*" "\\1" VERSION_NUMBER_MINOR "${VERSION_NUMBER}")
 math(EXPR VERSION_NUMBER_INTEGER
   "${VERSION_NUMBER_MAJOR}*100 + ${VERSION_NUMBER_MINOR}")
+# 4.1 broke backcompat in drsyms + 64-bit core (opcodes + reachability)
 # 4.0 broke backcompat in drmgr, drsyms, drinjectlib, and dr_get_milliseconds()
-set(OLDEST_COMPATIBLE_VERSION "400")
+set(OLDEST_COMPATIBLE_VERSION "401")
 
 # i#955: a Windows version of ELF DT_RPATH where a local file stores lib paths
 set(DR_RPATH_SUFFIX "drpath")
diff --git a/make/DynamoRIOConfigVersion.cmake.in b/make/DynamoRIOConfigVersion.cmake.in
index 3889bb2d863..44ad0a1f5c1 100644
--- a/make/DynamoRIOConfigVersion.cmake.in
+++ b/make/DynamoRIOConfigVersion.cmake.in
@@ -1,5 +1,5 @@
 # **********************************************************
-# Copyright (c) 2010-2012 Google, Inc.    All rights reserved.
+# Copyright (c) 2010-2013 Google, Inc.    All rights reserved.
 # Copyright (c) 2009-2010 VMware, Inc.    All rights reserved.
 # **********************************************************
 
@@ -47,7 +47,7 @@ elseif ("${PACKAGE_FIND_VERSION_MAJOR}" LESS @VERSION_NUMBER_MAJOR@)
     set(PACKAGE_VERSION_COMPATIBLE 1)
   endif ("${PACKAGE_FIND_VERSION_MAJOR}" LESS 3)
 elseif ("${PACKAGE_FIND_VERSION_MAJOR}" EQUAL @VERSION_NUMBER_MAJOR@)
-  # Asking for lesser minor version == backward compatible
+  # Asking for lesser minor version == backward compatible in general
   if ("${PACKAGE_FIND_VERSION_MINOR}" EQUAL @VERSION_NUMBER_MINOR@)
     if ("${PACKAGE_FIND_VERSION_COUNT}" GREATER 2)
       if ("${PACKAGE_FIND_VERSION_PATCH}" LESS @VERSION_NUMBER_PATCHLEVEL@)
@@ -61,7 +61,12 @@ elseif ("${PACKAGE_FIND_VERSION_MAJOR}" EQUAL @VERSION_NUMBER_MAJOR@)
       set(PACKAGE_VERSION_EXACT 1)
     endif ("${PACKAGE_FIND_VERSION_COUNT}" GREATER 2)
   elseif ("${PACKAGE_FIND_VERSION_MINOR}" LESS @VERSION_NUMBER_MINOR@)
-    set(PACKAGE_VERSION_COMPATIBLE 1)
+    if ("${PACKAGE_FIND_VERSION_MAJOR}" EQUAL 4 AND
+        "${PACKAGE_FIND_VERSION_MINOR}" EQUAL 0)
+      # 4.1 is incompatible with 4.0
+    else ()
+      set(PACKAGE_VERSION_COMPATIBLE 1)
+    endif ()
   else ()
     # We are relatively forward compatible except features we added
     # but better err on the side of caution