diff --git a/artiq/gateware/targets/kc705.py b/artiq/gateware/targets/kc705.py
index 0596efcd7..7a9bde597 100755
--- a/artiq/gateware/targets/kc705.py
+++ b/artiq/gateware/targets/kc705.py
@@ -226,6 +226,7 @@ class NIST_CLOCK(_NIST_Ions):
                                                    ofifo_depth=512,
                                                    ififo_depth=4))
 
+        self.config["HAS_RTIO_LOG"] = None
         self.config["RTIO_LOG_CHANNEL"] = len(rtio_channels)
         rtio_channels.append(rtio.LogChannel())
 
@@ -304,6 +305,7 @@ class NIST_QC2(_NIST_Ions):
                                                        ofifo_depth=512,
                                                        ififo_depth=4))
 
+        self.config["HAS_RTIO_LOG"] = None
         self.config["RTIO_LOG_CHANNEL"] = len(rtio_channels)
         rtio_channels.append(rtio.LogChannel())
 
diff --git a/artiq/gateware/targets/pipistrello.py b/artiq/gateware/targets/pipistrello.py
index b124b8f63..3a4d5beed 100755
--- a/artiq/gateware/targets/pipistrello.py
+++ b/artiq/gateware/targets/pipistrello.py
@@ -212,6 +212,7 @@ trce -v 12 -fastpaths -tsi {build_name}.tsi -o {build_name}.twr {build_name}.ncd
         rtio_channels.append(rtio.Channel.from_phy(
             phy, ofifo_depth=64, ififo_depth=64))
 
+        self.config["HAS_RTIO_LOG"] = None
         self.config["RTIO_LOG_CHANNEL"] = len(rtio_channels)
         rtio_channels.append(rtio.LogChannel())
 
diff --git a/artiq/runtime.rs/libksupport/rtio.rs b/artiq/runtime.rs/libksupport/rtio.rs
index 3f3a2f6ce..b98b9eaa6 100644
--- a/artiq/runtime.rs/libksupport/rtio.rs
+++ b/artiq/runtime.rs/libksupport/rtio.rs
@@ -123,6 +123,7 @@ pub extern fn input_data(channel: u32) -> u32 {
     }
 }
 
+#[cfg(has_rtio_log)]
 pub fn log(timestamp: i64, data: &[u8]) {
     unsafe {
         csr::rtio::chan_sel_write(csr::CONFIG_RTIO_LOG_CHANNEL);
@@ -144,3 +145,6 @@ pub fn log(timestamp: i64, data: &[u8]) {
         csr::rtio::o_we_write(1);
     }
 }
+
+#[cfg(not(has_rtio_log))]
+pub fn log(timestamp: i64, data: &[u8]) {}