--- libical-1.0/src/libical/orig.icaltimezone.c 2014-07-28 17:05:08.000000000 +0200
+++ libical-1.0/src/libical/icaltimezone.c      2014-07-28 17:07:13.000000000 +0200
@@ -47,7 +47,10 @@
 
 #ifdef HAVE_PTHREAD
 #include <pthread.h>
-static pthread_mutex_t builtin_mutex = PTHREAD_MUTEX_INITIALIZER;
+// static pthread_mutex_t builtin_mutex = PTHREAD_MUTEX_INITIALIZER;
+// It seems the same thread can attempt to lock builtin_mutex multiple times
+// (at least when using builtin tzdata), so make it builtin_mutex recursive:
+static pthread_mutex_t builtin_mutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
 #endif
 
 #ifdef WIN32