diff --git a/CMakeLists.txt b/CMakeLists.txt
index a55940eff..abb188577 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -274,6 +274,14 @@ endif()
 
 #### expose depends ####
 
+# check for change in arch (32<->64)
+if(UNIX)
+    GET_PROPERTY(DFHACK_CACHED_ARCH CACHE STRING PROPERTY DFHACK_BUILD_ARCH)
+	if(NOT "${DFHACK_BUILD_ARCH}" STREQUAL "${DFHACK_CACHED_ARCH}")
+        unset(ZLIB_LIBRARY CACHE)
+        unset(CMAKE_HAVE_PTHREAD_H CACHE)
+    endif()
+endif()
 
 # find and make available libz
 if(NOT UNIX) # Windows
diff --git a/depends/protobuf/CMakeLists.txt b/depends/protobuf/CMakeLists.txt
index 5b54c8335..9846fd4e5 100644
--- a/depends/protobuf/CMakeLists.txt
+++ b/depends/protobuf/CMakeLists.txt
@@ -68,7 +68,7 @@ IF (HAVE_HASH_MAP EQUAL 0)
 ENDIF()
 
 IF(UNIX)
-    FIND_PACKAGE(Threads)
+	FIND_PACKAGE(Threads REQUIRED)
 ENDIF()
 
 CONFIGURE_FILE("${CMAKE_CURRENT_SOURCE_DIR}/config.h.in" "${CMAKE_CURRENT_BINARY_DIR}/config.h")
@@ -247,4 +247,4 @@ IF(NOT CMAKE_CROSSCOMPILING)
     TARGET_LINK_LIBRARIES(protoc-bin protoc)
 
     EXPORT(TARGETS protoc-bin FILE ${CMAKE_BINARY_DIR}/ImportExecutables.cmake )
-ENDIF()
\ No newline at end of file
+ENDIF()