diff --git a/headers/os/kernel/OS.h b/headers/os/kernel/OS.h
index 3e04690a5b..f1eefd4b3d 100644
--- a/headers/os/kernel/OS.h
+++ b/headers/os/kernel/OS.h
@@ -25,9 +25,16 @@ extern "C" {
 #define B_INFINITE_TIMEOUT	(9223372036854775807LL)
 
 enum {
-	B_TIMEOUT			= 8,	/* relative timeout */
-	B_RELATIVE_TIMEOUT	= 8,	/* fails after a relative timeout with B_WOULD_BLOCK */
-	B_ABSOLUTE_TIMEOUT	= 16	/* fails after an absolute timeout with B_WOULD BLOCK */
+	B_TIMEOUT						= 0x8,	/* relative timeout */
+	B_RELATIVE_TIMEOUT				= 0x8,	/* fails after a relative timeout
+												with B_TIMED_OUT */
+	B_ABSOLUTE_TIMEOUT				= 0x10,	/* fails after an absolute timeout
+												with B_TIMED_OUT */
+
+	/* experimental Haiku only API */
+	B_TIMEOUT_REAL_TIME_BASE		= 0x40,
+	B_ABSOLUTE_REAL_TIME_TIMEOUT	= B_ABSOLUTE_TIMEOUT
+										| B_TIMEOUT_REAL_TIME_BASE
 };
 
 /*-------------------------------------------------------------*/
diff --git a/src/system/kernel/thread.cpp b/src/system/kernel/thread.cpp
index 56bc0adf8d..fca78b9e29 100644
--- a/src/system/kernel/thread.cpp
+++ b/src/system/kernel/thread.cpp
@@ -30,6 +30,7 @@
 #include <kimage.h>
 #include <kscheduler.h>
 #include <ksignal.h>
+#include <real_time_clock.h>
 #include <smp.h>
 #include <syscalls.h>
 #include <syscall_restart.h>
@@ -2271,8 +2272,14 @@ thread_block_with_timeout_locked(uint32 timeoutFlags, bigtime_t timeout)
 		// avoids nasty race conditions and deadlock problems that could
 		// otherwise occur between our cancel_timer() and a concurrently
 		// executing thread_block_timeout().
-		uint32 timerFlags = (timeoutFlags & B_RELATIVE_TIMEOUT)
-			? B_ONE_SHOT_RELATIVE_TIMER : B_ONE_SHOT_ABSOLUTE_TIMER;
+		uint32 timerFlags;
+		if ((timeoutFlags & B_RELATIVE_TIMEOUT) != 0) {
+			timerFlags = B_ONE_SHOT_RELATIVE_TIMER;
+		} else {
+			timerFlags = B_ONE_SHOT_ABSOLUTE_TIMER;
+			if ((timeoutFlags & B_TIMEOUT_REAL_TIME_BASE) != 0)
+				timeout -= rtc_boot_time();
+		}
 		timerFlags |= B_TIMER_ACQUIRE_THREAD_LOCK;
 
 		// install the timer