diff --git a/artiq/runtime.rs/src/kernel.rs b/artiq/runtime.rs/src/kernel.rs
index 8f796ebe5..f38e951f0 100644
--- a/artiq/runtime.rs/src/kernel.rs
+++ b/artiq/runtime.rs/src/kernel.rs
@@ -3,7 +3,7 @@ use board::csr;
 use mailbox;
 
 const KERNELCPU_EXEC_ADDRESS:    usize = 0x40400000;
-const KERNELCPU_LAST_ADDRESS:    usize = (0x4fffffff - 1024*1024);
+const KERNELCPU_LAST_ADDRESS:    usize = 0x4fffffff;
 const KSUPPORT_HEADER_SIZE:      usize = 0x80;
 
 pub unsafe fn start() {
diff --git a/artiq/runtime/ksupport.c b/artiq/runtime/ksupport.c
index 959d61623..8ec3185fc 100644
--- a/artiq/runtime/ksupport.c
+++ b/artiq/runtime/ksupport.c
@@ -18,7 +18,7 @@
 
 #define KERNELCPU_EXEC_ADDRESS    0x40400000
 #define KERNELCPU_PAYLOAD_ADDRESS 0x40420000
-#define KERNELCPU_LAST_ADDRESS    (0x4fffffff - 1024*1024)
+#define KERNELCPU_LAST_ADDRESS    0x4fffffff
 #define KSUPPORT_HEADER_SIZE      0x80
 
 double round(double x);