diff --git a/lib/krb5/heim_threads.h b/lib/krb5/heim_threads.h
index d9eb9f6f3..37d3f9818 100644
--- a/lib/krb5/heim_threads.h
+++ b/lib/krb5/heim_threads.h
@@ -81,6 +81,8 @@
 
 #elif defined(ENABLE_PTHREAD_SUPPORT) && !defined(__NetBSD__)
 
+#include <pthread.h>
+
 #define HEIMDAL_MUTEX pthread_mutex_t
 #define HEIMDAL_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
 #define HEIMDAL_MUTEX_init(m) pthread_mutex_init(m, NULL)