diff --git a/include/openmc/error.h b/include/openmc/error.h
index 4c4efe6a73..0537834463 100644
--- a/include/openmc/error.h
+++ b/include/openmc/error.h
@@ -10,7 +10,7 @@
 #include "openmc/capi.h"
 #include "openmc/settings.h"
 
-#ifdef __GNUC__
+#if defined(__GNUC__) || defined(__clang__)
 #define UNREACHABLE() __builtin_unreachable()
 #else
 #define UNREACHABLE() (void)0
diff --git a/src/tallies/trigger.cpp b/src/tallies/trigger.cpp
index 56f5c4c563..40eb3290fe 100644
--- a/src/tallies/trigger.cpp
+++ b/src/tallies/trigger.cpp
@@ -87,6 +87,8 @@ check_tally_triggers(double& ratio, int& tally_id, int& score)
             case TriggerMetric::relative_error:
               uncertainty = rel_err;
               break;
+            case TriggerMetric::not_active:
+              UNREACHABLE();
           }
 
           // Compute the uncertainty / threshold ratio.