diff --git a/tests/test_check.c b/tests/test_check.c
index e059130d..cbe6917d 100644
--- a/tests/test_check.c
+++ b/tests/test_check.c
@@ -12,6 +12,7 @@
 ///////////////////////////////////////////////////////////////////////////////
 
 #include "tests.h"
+#include "mythread.h"
 
 
 // These must be specified as numbers so that the test works on EBCDIC
diff --git a/tests/test_hardware.c b/tests/test_hardware.c
index 17c51da2..ee4434c1 100644
--- a/tests/test_hardware.c
+++ b/tests/test_hardware.c
@@ -15,6 +15,7 @@
 ///////////////////////////////////////////////////////////////////////////////
 
 #include "tests.h"
+#include "mythread.h"
 
 
 static void
diff --git a/tests/test_memlimit.c b/tests/test_memlimit.c
index 6e2e62e1..b5f91472 100644
--- a/tests/test_memlimit.c
+++ b/tests/test_memlimit.c
@@ -11,6 +11,7 @@
 ///////////////////////////////////////////////////////////////////////////////
 
 #include "tests.h"
+#include "mythread.h"
 
 
 #define MEMLIMIT_TOO_LOW 1234U