diff --git a/artiq/devices/runtime.py b/artiq/devices/runtime.py
index a4a55f77f..5f84fc52e 100644
--- a/artiq/devices/runtime.py
+++ b/artiq/devices/runtime.py
@@ -10,6 +10,7 @@ _syscalls = {
     "rpc": "i+:i",
     "gpio_set": "ii:n",
     "rtio_set": "Iii:n",
+    "rtio_replace": "Iii:n",
     "rtio_sync": "i:n",
     "dds_program": "ii:n",
 }
diff --git a/soc/runtime/rtio.c b/soc/runtime/rtio.c
index ff65b5b79..550e54e45 100644
--- a/soc/runtime/rtio.c
+++ b/soc/runtime/rtio.c
@@ -17,6 +17,14 @@ void rtio_set(long long int timestamp, int channel, int value)
     rtio_o_we_write(1);
 }
 
+void rtio_replace(long long int timestamp, int channel, int value)
+{
+    rtio_chan_sel_write(channel);
+    rtio_o_timestamp_write(timestamp);
+    rtio_o_value_write(value);
+    rtio_o_replace_write(1);
+}
+
 void rtio_sync(int channel)
 {
     rtio_chan_sel_write(channel);
diff --git a/soc/runtime/rtio.h b/soc/runtime/rtio.h
index 2ed47058e..619ee9890 100644
--- a/soc/runtime/rtio.h
+++ b/soc/runtime/rtio.h
@@ -3,6 +3,7 @@
 
 void rtio_init(void);
 void rtio_set(long long int timestamp, int channel, int value);
+void rtio_replace(long long int timestamp, int channel, int value);
 void rtio_sync(int channel);
 
 #endif /* __RTIO_H */
diff --git a/soc/runtime/symbols.c b/soc/runtime/symbols.c
index 5f04ce347..c2db7bcdd 100644
--- a/soc/runtime/symbols.c
+++ b/soc/runtime/symbols.c
@@ -11,6 +11,7 @@ static const struct symbol syscalls[] = {
     {"rpc", rpc},
     {"gpio_set", gpio_set},
     {"rtio_set", rtio_set},
+    {"rtio_replace", rtio_replace},
     {"rtio_sync", rtio_sync},
     {"dds_program", dds_program},
     {NULL, NULL}