diff --git a/src/Makefile.am b/src/Makefile.am
index bd42cac..46d46f5 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -24,6 +24,6 @@ TR_CLASS = memory.c \
 lib_LTLIBRARIES = libtrbase.la
 
 libtrbase_la_SOURCES = $(TR_CLASS)
-libtrbase_la_CFLAGS  = $(AM_CFLAGS)
+libtrbase_la_CFLAGS  = $(AM_CFLAGS) -lpthread
 libtrbase_la_LIBADD  =
 libtrbase_la_LDFLAGS = -version-info 1:0:1
diff --git a/src/memory.c b/src/memory.c
index 1d3d97f..4d109a8 100644
--- a/src/memory.c
+++ b/src/memory.c
@@ -48,6 +48,7 @@
 
 #include <stdio.h>
 
+#include <pthread.h>
 #include <stdlib.h>
 #include <string.h>
 #include <search.h>
@@ -377,6 +378,8 @@ TR_reference(void * mem)
 	return mem;
 }
 
+pthread_mutex_t TR_memop_lock = PTHREAD_MUTEX_INITIALIZER;
+
 /*
  * This tries to reflect the memory management behaviour of the
  * GNU version of malloc. For other versions this might need
@@ -435,7 +438,9 @@ TR_malloc(size_t size)
 	}
 
 #ifdef MEM_OPT
+	pthread_mutex_lock(&TR_memop_lock);
 	seg = deleteElement(&segments, size);
+	pthread_mutex_unlock(&TR_memop_lock);
 #endif
 
 	if (NULL == seg) {
@@ -474,7 +479,9 @@ TR_free(void ** mem)
 			seg->ref_count--;
 		} else {
 #ifdef MEM_OPT
+			pthread_mutex_lock(&TR_memop_lock);
 			insertElement(&segments, seg);
+			pthread_mutex_unlock(&TR_memop_lock);
 #else
 			free(seg);
 #endif