diff --git a/core/src/main/resources/lib/c/reactor-c b/core/src/main/resources/lib/c/reactor-c
index 587a8f9498..33e7c20ddb 160000
--- a/core/src/main/resources/lib/c/reactor-c
+++ b/core/src/main/resources/lib/c/reactor-c
@@ -1 +1 @@
-Subproject commit 587a8f9498b69bc82f404e432f881d7bb0bcf383
+Subproject commit 33e7c20ddb052e9370e66b32a8232dd8195d6bb7
diff --git a/test/C/src/modal_models/ModesWithWatchdog.lf b/test/C/src/modal_models/ModesWithWatchdog.lf
new file mode 100644
index 0000000000..8cec971ff5
--- /dev/null
+++ b/test/C/src/modal_models/ModesWithWatchdog.lf
@@ -0,0 +1,46 @@
+/**
+ * When in the Primary mode, the watchdog is sure to trigger, causing the reaction to watcher
+ * to be executed one microstep later.  Previously, after a mode transition, the microstep was
+ * hardwired to 1, which caused a fatal error after the mode transition when the runtime tried
+ * to advance to microstep 1 and found that it was already at microstep 1.  This program tests
+ * that this is fixed.  Success is simply running to completion without error.
+ */
+target C {
+  keepalive: true,
+  timeout: 1 s
+}
+
+reactor Arbitrator(timeout: time = 100 ms) {
+  input in1: double
+  input in2: double
+
+  watchdog watcher(timeout) {= lf_print("watchdog timeout."); =}
+
+  initial mode Primary {
+    reaction(in1) -> watcher {=
+      lf_watchdog_start(watcher, 0);
+    =}
+
+    reaction(watcher) -> reset(Backup) {=
+      lf_print("watchdog reaction.");
+      lf_set_mode(Backup);
+    =}
+  }
+
+  mode Backup {
+    reaction(in2) -> watcher {=
+      lf_watchdog_start(watcher, 0);
+    =}
+  }
+}
+
+main reactor {
+  timer t(0, 100 ms)
+
+  ar = new Arbitrator()
+
+  reaction(t) -> ar.in1, ar.in2 {=
+    lf_set(ar.in1, 0.0);
+    lf_set(ar.in2, 0.0);
+  =}
+}