diff --git a/CHANGES b/CHANGES
index 265f674115..26ce4fe4db 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,4 +1,15 @@
 
+2.6-591 | 2019-07-11 13:29:28 -0700
+
+  * Fix potential thread safety issue with zeekenv util function
+
+    Observed segfault accessing the local static std::map of zeekenv() from
+    a logging thread, but only in non-debug builds using Apple/Clang
+    compiler, not in a debug build or GCC.  Don't quite get this behavior
+    since static local variable initialization is supposed to be thread-safe
+    since C++11, but moving to a global static works and is "more efficient"
+    anyway since there's no longer any run-time overhead. (Jon Siwek, Corelight)
+
 2.6-589 | 2019-07-11 13:14:52 -0700
 
   * GH-421: fix bugs/regressions in DNP3 analyzer (Hui Lin)
diff --git a/VERSION b/VERSION
index 2e1ccaed09..ab6fd2fbdb 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.6-589
+2.6-591
diff --git a/src/util.cc b/src/util.cc
index f2735ad29a..e7d989660b 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -1842,24 +1842,24 @@ void bro_strerror_r(int bro_errno, char* buf, size_t buflen)
 	strerror_r_helper(res, buf, buflen);
 	}
 
+static const std::map<const char*, const char*, CompareString> legacy_vars = {
+	{ "ZEEKPATH", "BROPATH" },
+	{ "ZEEK_PLUGIN_PATH", "BRO_PLUGIN_PATH" },
+	{ "ZEEK_PLUGIN_ACTIVATE", "BRO_PLUGIN_ACTIVATE" },
+	{ "ZEEK_PREFIXES", "BRO_PREFIXES" },
+	{ "ZEEK_DNS_FAKE", "BRO_DNS_FAKE" },
+	{ "ZEEK_SEED_FILE", "BRO_SEED_FILE" },
+	{ "ZEEK_LOG_SUFFIX", "BRO_LOG_SUFFIX" },
+	{ "ZEEK_PROFILER_FILE", "BRO_PROFILER_FILE" },
+	{ "ZEEK_DISABLE_ZEEKYGEN", "BRO_DISABLE_BROXYGEN" },
+	{ "ZEEK_DEFAULT_CONNECT_RETRY", "BRO_DEFAULT_CONNECT_RETRY" },
+	{ "ZEEK_BROKER_MAX_THREADS", "BRO_BROKER_MAX_THREADS" },
+	{ "ZEEK_DEFAULT_LISTEN_ADDRESS", "BRO_DEFAULT_LISTEN_ADDRESS" },
+	{ "ZEEK_DEFAULT_LISTEN_RETRY", "BRO_DEFAULT_LISTEN_RETRY" },
+};
+
 char* zeekenv(const char* name)
 	{
-	static std::map<const char*, const char*, CompareString> legacy_vars = {
-		{ "ZEEKPATH", "BROPATH" },
-		{ "ZEEK_PLUGIN_PATH", "BRO_PLUGIN_PATH" },
-		{ "ZEEK_PLUGIN_ACTIVATE", "BRO_PLUGIN_ACTIVATE" },
-		{ "ZEEK_PREFIXES", "BRO_PREFIXES" },
-		{ "ZEEK_DNS_FAKE", "BRO_DNS_FAKE" },
-		{ "ZEEK_SEED_FILE", "BRO_SEED_FILE" },
-		{ "ZEEK_LOG_SUFFIX", "BRO_LOG_SUFFIX" },
-		{ "ZEEK_PROFILER_FILE", "BRO_PROFILER_FILE" },
-		{ "ZEEK_DISABLE_ZEEKYGEN", "BRO_DISABLE_BROXYGEN" },
-		{ "ZEEK_DEFAULT_CONNECT_RETRY", "BRO_DEFAULT_CONNECT_RETRY" },
-		{ "ZEEK_BROKER_MAX_THREADS", "BRO_BROKER_MAX_THREADS" },
-		{ "ZEEK_DEFAULT_LISTEN_ADDRESS", "BRO_DEFAULT_LISTEN_ADDRESS" },
-		{ "ZEEK_DEFAULT_LISTEN_RETRY", "BRO_DEFAULT_LISTEN_RETRY" },
-	};
-
 	auto rval = getenv(name);
 
 	if ( rval )