diff --git a/src/arch/abtd_env.c b/src/arch/abtd_env.c
index 9b564d44..42e33a19 100644
--- a/src/arch/abtd_env.c
+++ b/src/arch/abtd_env.c
@@ -23,9 +23,9 @@
 /* To avoid potential overflow, we intentionally use a smaller value than the
  * real limit. */
 #define ABTD_ENV_INT_MAX ((int)(INT_MAX / 2))
-#define ABTD_ENV_UINT32_MAX ((int)(UINT32_MAX / 2))
-#define ABTD_ENV_UINT64_MAX ((int)(UINT64_MAX / 2))
-#define ABTD_ENV_SIZE_MAX ((int)(SIZE_MAX / 2))
+#define ABTD_ENV_UINT32_MAX ((uint32_t)(UINT32_MAX / 2))
+#define ABTD_ENV_UINT64_MAX ((uint64_t)(UINT64_MAX / 2))
+#define ABTD_ENV_SIZE_MAX ((size_t)(SIZE_MAX / 2))
 
 static uint32_t roundup_pow2_uint32(uint32_t val);
 #ifdef ABT_CONFIG_USE_MEM_POOL
diff --git a/src/include/abtu.h b/src/include/abtu.h
index afb07c5d..f297edaa 100644
--- a/src/include/abtu.h
+++ b/src/include/abtu.h
@@ -112,18 +112,24 @@ static inline size_t ABTU_roundup_size(size_t val, size_t multiple)
 #define ABTU_unlikely(cond) (cond)
 #endif
 
-#ifdef HAVE___BUILTIN_UNREACHABLE
-#define ABTU_unreachable() __builtin_unreachable()
-#else
-#define ABTU_unreachable()
-#endif
-
 #ifdef HAVE_FUNC_ATTRIBUTE_NORETURN
 #define ABTU_noreturn __attribute__((noreturn))
 #else
 #define ABTU_noreturn
 #endif
 
+#ifdef HAVE___BUILTIN_UNREACHABLE
+#define ABTU_unreachable() __builtin_unreachable()
+#else
+/* abort is better than entering an unknown area.  First assert(0), which shows
+ * something if assert() is enabled.  If assert() is disabled, let's abort(). */
+static inline ABTU_noreturn void ABTU_unreachable(void)
+{
+    assert(0);
+    abort();
+}
+#endif
+
 #ifdef ABT_CONFIG_HAVE_ALIGNOF_GCC
 #define ABTU_alignof(type) (__alignof__(type))
 #elif defined(ABT_CONFIG_HAVE_ALIGNOF_C11)
diff --git a/src/info.c b/src/info.c
index 8e019559..b3864228 100644
--- a/src/info.c
+++ b/src/info.c
@@ -372,7 +372,6 @@ int ABT_info_query_config(ABT_info_query_kind query_kind, void *val)
             break;
         default:
             ABTI_HANDLE_ERROR(ABT_ERR_INV_QUERY_KIND);
-            break;
     }
     return ABT_SUCCESS;
 }
diff --git a/src/thread.c b/src/thread.c
index 59974765..aac05d15 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -484,6 +484,9 @@ int ABT_thread_free_many(int num_threads, ABT_thread *thread_list)
 
     for (i = 0; i < num_threads; i++) {
         ABTI_thread *p_thread = ABTI_thread_get_ptr(thread_list[i]);
+        thread_list[i] = ABT_THREAD_NULL;
+        if (!p_thread)
+            continue;
         /* TODO: check input */
         thread_join(&p_local, p_thread);
         ABTI_thread_free(p_global, p_local, p_thread);
@@ -582,8 +585,11 @@ int ABT_thread_join_many(int num_threads, ABT_thread *thread_list)
     ABTI_local *p_local = ABTI_local_get_local();
     int i;
     for (i = 0; i < num_threads; i++) {
+        ABTI_thread *p_thread = ABTI_thread_get_ptr(thread_list[i]);
+        if (!p_thread)
+            continue;
         /* TODO: check input */
-        thread_join(&p_local, ABTI_thread_get_ptr(thread_list[i]));
+        thread_join(&p_local, p_thread);
     }
     return ABT_SUCCESS;
 }
diff --git a/test/util/abttest.c b/test/util/abttest.c
index ca535f8e..efd6f810 100644
--- a/test/util/abttest.c
+++ b/test/util/abttest.c
@@ -221,9 +221,6 @@ void ATS_read_args(int argc, char **argv)
 
 int ATS_get_arg_val(ATS_arg arg)
 {
-    if (arg < ATS_ARG_N_ES || (int)arg >= NUM_ARG_KINDS) {
-        return 0;
-    }
     return g_arg_val[arg];
 }
 
@@ -344,14 +341,15 @@ static inline size_t ABT_tool_unit_entry_table_index(const void *unit)
         uint32_t val2 = val ^ (val >> 16);
         return (val2 ^ (val2 >> 8)) &
                (ATS_TOOL_UNIT_ENTRY_TABLE_NUM_ENTIRES - 1);
-    } else if (sizeof(void *) == 8) {
+    } else {
+        /* We support only 32-bit or 64-bit pointer sizes. */
+        assert(sizeof(void *) == 8);
         uint64_t val = (uint64_t)(uintptr_t)unit;
         uint64_t val2 = val ^ (val >> 32);
         uint64_t val3 = val2 ^ (val2 >> 16);
         return (val3 ^ (val3 >> 8)) &
                (ATS_TOOL_UNIT_ENTRY_TABLE_NUM_ENTIRES - 1);
     }
-    return 0;
 }
 
 static ATS_tool_unit_entry *ATS_tool_get_unit_entry(const void *unit)