diff --git a/lib/ssm/include/ssm.h b/lib/ssm/include/ssm.h
index 9e3d9e40..5e59531a 100644
--- a/lib/ssm/include/ssm.h
+++ b/lib/ssm/include/ssm.h
@@ -68,6 +68,15 @@ See [the detailed documentation](@ref all)
 #define SSM_ACT_FREE(ptr, size) free(ptr)
 #endif
 
+/** Underlying exception handler; can be overridden by each platform
+ *
+ * ssm_throw is declared as a weak symbol, meaning it will be left a null
+ * pointer if the linker does not find a definition for this symbol in any
+ * object file.
+ */
+void ssm_throw(int reason, const char *file, int line, const char *func)
+  __attribute__((weak));
+
 /** Invoked when a process must terminate, e.g., when memory or queue space is
  * exhausted. Not expected to return.
  *
@@ -76,13 +85,12 @@ See [the detailed documentation](@ref all)
  * overridden by defining ssm_throw.
  */
 #define SSM_THROW(reason) \
-  ssm_throw ? \
-    ssm_throw(reason, __FILE__, __LINE__, __func__) : \
-    exit(reason)
-
-/** Underlying crash handler; can be overriden. */
-void ssm_throw(int reason, const char *file, int line, const char *func)
-  __attribute__((weak));
+    do \
+      if (ssm_throw) \
+        ssm_throw(reason, __FILE__, __LINE__, __func__); \
+      else \
+        for(;;); \
+    while (0)
 
 /** Error codes, indicating reason for failure.
  *
diff --git a/lib/ssm/src/ssm-scheduler.c b/lib/ssm/src/ssm-scheduler.c
index 9ae6c160..35fb3b53 100644
--- a/lib/ssm/src/ssm-scheduler.c
+++ b/lib/ssm/src/ssm-scheduler.c
@@ -297,14 +297,14 @@ void ssm_unschedule(ssm_sv_t *var)
     q_idx_t hole = find_queued_event(var);
     var->later_time = SSM_NEVER;
     ssm_sv_t *moved_var = event_queue[event_queue_len--];
-    if (hole < SSM_QUEUE_HEAD + event_queue_len) {
-      // Percolate if removal led to hole in the queue.
+    if (hole < SSM_QUEUE_HEAD + event_queue_len)
+      // Percolate only if removal led to a hole in the queue; no need to do
+      // this if we happened to remove the last element of the queue.
       if (hole == SSM_QUEUE_HEAD ||
           event_queue[hole >> 1]->later_time < moved_var->later_time)
         event_queue_percolate_down(hole, moved_var);
       else
         event_queue_percolate_up(hole, moved_var);
-    }
   }
 }