diff --git a/artiq/firmware/bootloader/main.rs b/artiq/firmware/bootloader/main.rs
index 1ef7426a1..9a41bdb4b 100644
--- a/artiq/firmware/bootloader/main.rs
+++ b/artiq/firmware/bootloader/main.rs
@@ -17,7 +17,7 @@ use board_misoc::slave_fpga;
 #[cfg(has_ethmac)]
 use board_misoc::{clock, ethmac, net_settings};
 use board_misoc::uart_console::Console;
-use riscv::register::{mcause, mepc};
+use riscv::register::{mcause, mepc, mtval};
 
 fn check_integrity() -> bool {
     extern {
@@ -522,7 +522,8 @@ pub extern fn main() -> i32 {
 pub extern fn exception(_regs: *const u32) {
     let pc = mepc::read();
     let cause = mcause::read().cause();
-    panic!("{:?} at PC {:#08x}", cause, u32::try_from(pc).unwrap())
+    let mtval = mtval::read();
+    panic!("{:?} at PC {:#08x}, trap value {:#08x}", cause, u32::try_from(pc).unwrap(), mtval);
 }
 
 #[no_mangle]
diff --git a/artiq/firmware/ksupport/lib.rs b/artiq/firmware/ksupport/lib.rs
index f4a0ec2c7..d915d7e81 100644
--- a/artiq/firmware/ksupport/lib.rs
+++ b/artiq/firmware/ksupport/lib.rs
@@ -532,7 +532,8 @@ pub unsafe fn main() {
 pub extern fn exception(_regs: *const u32) {
     let pc = mepc::read();
     let cause = mcause::read().cause();
-    panic!("{:?} at PC {:#08x}", cause, u32::try_from(pc).unwrap())
+    let mtval = mtval::read();
+    panic!("{:?} at PC {:#08x}, trap value {:#08x}", cause, u32::try_from(pc).unwrap(), mtval);
 }
 
 #[no_mangle]
diff --git a/artiq/firmware/runtime/main.rs b/artiq/firmware/runtime/main.rs
index 04af01be0..45fb76f91 100644
--- a/artiq/firmware/runtime/main.rs
+++ b/artiq/firmware/runtime/main.rs
@@ -40,7 +40,7 @@ use proto_artiq::{mgmt_proto, moninj_proto, rpc_proto, session_proto, kernel_pro
 #[cfg(has_rtio_analyzer)]
 use proto_artiq::analyzer_proto;
 
-use riscv::register::{mcause, mepc};
+use riscv::register::{mcause, mepc, mtval};
 
 mod rtio_clocking;
 mod rtio_mgt;
@@ -319,7 +319,8 @@ pub extern fn exception(regs: *const TrapFrame) {
             }
 
             hexdump(u32::try_from(pc).unwrap());
-            panic!("exception {:?} at PC 0x{:x}", e, u32::try_from(pc).unwrap())
+            let mtval = mtval::read();
+            panic!("exception {:?} at PC 0x{:x}, trap value 0x{:x}", e, u32::try_from(pc).unwrap(), mtval)
         }
     }
 }
diff --git a/artiq/firmware/satman/main.rs b/artiq/firmware/satman/main.rs
index ef639b7f1..e0ec83612 100644
--- a/artiq/firmware/satman/main.rs
+++ b/artiq/firmware/satman/main.rs
@@ -18,7 +18,7 @@ use board_artiq::{spi, drtioaux};
 use board_artiq::drtio_routing;
 #[cfg(has_hmc830_7043)]
 use board_artiq::hmc830_7043;
-use riscv::register::{mcause, mepc};
+use riscv::register::{mcause, mepc, mtval};
 
 mod repeater;
 #[cfg(has_jdcg)]
@@ -670,7 +670,8 @@ pub extern fn exception(_regs: *const u32) {
     }
 
     hexdump(u32::try_from(pc).unwrap());
-    panic!("exception {:?} at PC 0x{:x}", cause, u32::try_from(pc).unwrap())
+    let mtval = mtval::read();
+    panic!("exception {:?} at PC 0x{:x}, trap value 0x{:x}", cause, u32::try_from(pc).unwrap(), mtval)
 }
 
 #[no_mangle]