diff --git a/CMakeLists.txt b/CMakeLists.txt
index 73dc2d3ee28..5139cb3b4c9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -804,7 +804,7 @@ if (Threads_FOUND)
   # Comment out check for C11 threads for now, since it conflicts with the
   # current --std=c99 compile flags at configuration time.  When we switch to
   # --std=c11, this can be uncommented.
-  #CHECK_INCLUDE_FILE("threads.h" HAVE_THREADS_H)
+  CHECK_INCLUDE_FILE("threads.h" HAVE_THREADS_H)
   if (WIN32)
     # When Win32 is available, we use those threads
     set (H5_HAVE_WIN_THREADS 1)
diff --git a/configure.ac b/configure.ac
index 72bc8f91b76..82a3febf370 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2237,7 +2237,7 @@ if test "X$THREADS" = "Xyes"; then
     # Comment out check for C11 threads for now, since it conflicts with the
     # current --std=c99 compile flags at configuration time.  When we switch to
     # --std=c11, this can be uncommented.
-    #AC_CHECK_HEADERS([threads.h],[HAVE_THREADS_H="yes"],[HAVE_THREADS_H="no"])
+    AC_CHECK_HEADERS([threads.h],[HAVE_THREADS_H="yes"],[HAVE_THREADS_H="no"])
     if test "x$HAVE_THREADS_H" = "xyes"; then
         # Default or no --> C11 threads
         if test "$withval" = "default" -o "$withval" = "no" ; then
diff --git a/src/H5private.h b/src/H5private.h
index e253bdd5076..466f46a3074 100644
--- a/src/H5private.h
+++ b/src/H5private.h
@@ -1130,8 +1130,8 @@ extern char H5_lib_vers_info_g[];
 #define H5CANCEL_DECL       /* */
 
 /* Disable & restore canceling the thread */
-#define H5TS_DISABLE_CANCEL /* */
-#define H5TS_RESTORE_CANCEL /* */
+#define H5TS_DISABLE_CANCEL do {} while(0)      /* no-op */
+#define H5TS_RESTORE_CANCEL do {} while(0)      /* no-op */
 #endif
 
 #ifdef H5_HAVE_THREADSAFE
@@ -1181,8 +1181,8 @@ extern char H5_lib_vers_info_g[];
 #define H5DLFTT_DECL  /* */
 
 /* No locks (non-threadsafe builds) */
-#define H5_API_LOCK   /* */
-#define H5_API_UNLOCK /* */
+#define H5_API_LOCK   do {} while(0)    /* no-op */
+#define H5_API_UNLOCK do {} while(0)    /* no-op */
 
 #endif /* H5_HAVE_THREADSAFE_API */