diff --git a/test/run-tests.py b/test/run-tests.py
index 2eb7ebbf4a..96ba81ec28 100755
--- a/test/run-tests.py
+++ b/test/run-tests.py
@@ -177,6 +177,10 @@ def Decode(s):
 
     expected_lines = [Decode(line) for line in expected.splitlines() if line]
     actual_lines = [Decode(line) for line in actual.splitlines() if line]
+
+    expected_lines = [line for line in expected_lines if not line.startswith("##")]
+    actual_lines = [line for line in actual_lines if not line.startswith("##")]
+
     return list(
         difflib.unified_diff(expected_lines, actual_lines, fromfile='expected',
                              tofile='actual', lineterm=''))
diff --git a/test/spec-wasm2c-prefix.c b/test/spec-wasm2c-prefix.c
index bc86f8fd4e..89583a447c 100644
--- a/test/spec-wasm2c-prefix.c
+++ b/test/spec-wasm2c-prefix.c
@@ -448,8 +448,9 @@ static void posix_install_signal_handler(void) {
   ss.ss_sp = malloc(SIGSTKSZ);
   ss.ss_flags = 0;
   ss.ss_size = SIGSTKSZ;
+  printf("##sigaltstack specsetup: %p, NULL\n", &ss);
   if (sigaltstack(&ss, NULL) != 0) {
-    perror("sigaltstack failed");
+    perror("sigaltstack specsetup failed");
     abort();
   }
 
@@ -478,8 +479,9 @@ static void posix_cleanup_signal_handler(void) {
   /* disable and free altstack */
   stack_t ss;
   ss.ss_flags = SS_DISABLE;
+  printf("##sigaltstack specshutdown: %p, NULL\n", &ss);
   if (sigaltstack(&ss, NULL) != 0) {
-    perror("sigaltstack failed");
+    perror("sigaltstack specshutdown failed");
     abort();
   }
   free(ss.ss_sp);
diff --git a/wasm2c/README.md b/wasm2c/README.md
index b7ab3bca2e..9fc620d3ce 100644
--- a/wasm2c/README.md
+++ b/wasm2c/README.md
@@ -720,3 +720,16 @@ void w2c_host_buf_done(w2c_host* instance, u32 ptr, u32 size) {
   printf("%s -> %.*s\n", instance->input, (int)size, &instance->memory.data[ptr]);
 }
 ```
+## Troubleshooting
+
+```
+error: No definition for WASM_RT_THREAD_LOCAL for this platform.
+```
+
+If you see the above error, wasm2c does not know how to define thread_local variables in your platform. You can address this in one of three ways
+
+1. If your compiler supports C11, pass in `-std=c11` as a compilation flag. Otherwise, you can either
+
+2. If you know how to define thread local variables in your compiler, define `WASM_RT_THREAD_LOCAL` macro as a compilation flag with the correct thread_local keywords. e.g., `-DWASM_RT_THREAD_LOCAL=__thread`
+
+3. If you can guarantee that at most one thread of your application will be running wasm2c sandboxes at any given time, you can pass the flag `-DWASM_RT_SINGLE_THREAD_ONLY` to simply define thread_local variables as global values.
diff --git a/wasm2c/wasm-rt-impl.c b/wasm2c/wasm-rt-impl.c
index e7d99cce8f..8379142d01 100644
--- a/wasm2c/wasm-rt-impl.c
+++ b/wasm2c/wasm-rt-impl.c
@@ -168,8 +168,9 @@ static void os_cleanup_signal_handler(void) {
 static bool os_has_altstack_installed() {
   /* check for altstack already in place */
   stack_t ss;
+  // printf("##sigaltstack check: NULL, %p\n", &ss);
   if (sigaltstack(NULL, &ss) != 0) {
-    perror("sigaltstack failed");
+    perror("sigaltstack check failed");
     abort();
   }
 
@@ -198,8 +199,9 @@ static void os_allocate_and_install_altstack(void) {
   ss.ss_sp = g_alt_stack;
   ss.ss_flags = 0;
   ss.ss_size = SIGSTKSZ;
+  // printf("##sigaltstack install: %p, NULL\n", &ss);
   if (sigaltstack(&ss, NULL) != 0) {
-    perror("sigaltstack failed");
+    perror("sigaltstack install failed");
     abort();
   }
 }
@@ -211,22 +213,24 @@ static void os_disable_and_deallocate_altstack(void) {
 
   /* verify altstack was still in place */
   stack_t ss;
+  // printf("##sigaltstack dealloc: NULL, %p\n", &ss);
   if (sigaltstack(NULL, &ss) != 0) {
-    perror("sigaltstack failed");
+    perror("sigaltstack dealloc check failed");
     abort();
   }
 
   if ((!g_alt_stack) || (ss.ss_flags & SS_DISABLE) ||
       (ss.ss_sp != g_alt_stack) || (ss.ss_size != SIGSTKSZ)) {
-    DEBUG_PRINTF(
+    printf(
         "wasm-rt warning: alternate stack was modified unexpectedly\n");
     return;
   }
 
   /* disable and free */
   ss.ss_flags = SS_DISABLE;
+  // printf("##sigaltstack free: %p, NULL\n", &ss);
   if (sigaltstack(&ss, NULL) != 0) {
-    perror("sigaltstack failed");
+    perror("sigaltstack free failed");
     abort();
   }
   assert(!os_has_altstack_installed());
diff --git a/wasm2c/wasm-rt.h b/wasm2c/wasm-rt.h
index d58a37b812..efb8640ad9 100644
--- a/wasm2c/wasm-rt.h
+++ b/wasm2c/wasm-rt.h
@@ -75,15 +75,19 @@ extern "C" {
 
 #endif
 
+#ifndef WASM_RT_THREAD_LOCAL
 #ifdef WASM_RT_C11_AVAILABLE
 #define WASM_RT_THREAD_LOCAL _Thread_local
 #elif defined(_MSC_VER)
 #define WASM_RT_THREAD_LOCAL __declspec(thread)
-#elif (defined(__GNUC__) || defined(__clang__)) && !defined(__APPLE__)
+#elif defined(__GNUC__) || defined(__clang__)
 // Disabled on Apple systems due to sporadic test failures.
 #define WASM_RT_THREAD_LOCAL __thread
-#else
+#elif WASM_RT_SINGLE_THREAD_ONLY
 #define WASM_RT_THREAD_LOCAL
+#else
+#error "No definition for WASM_RT_THREAD_LOCAL for this platform."
+#endif
 #endif
 
 /**