diff --git a/moo/configure b/moo/configure
index f6da54c..0d171ff 100755
--- a/moo/configure
+++ b/moo/configure
@@ -21530,7 +21530,7 @@ fi
 
 if test "x${enable_libunwind_is}" = "xyes"
 then
-	if test "x${ac_cv_header_unwind_h}" = "xyes"  -a "${UNWIND_LIBS}" != ""
+	if test "x${ac_cv_header_libunwind_h}" = "xyes"  -a "${UNWIND_LIBS}" != ""
 	then
 
 $as_echo "#define MOO_ENABLE_LIBUNWIND /**/" >>confdefs.h
diff --git a/moo/configure.ac b/moo/configure.ac
index 6818112..bcea909 100644
--- a/moo/configure.ac
+++ b/moo/configure.ac
@@ -745,7 +745,7 @@ AC_ARG_ENABLE([libunwind],
 )
 if test "x${enable_libunwind_is}" = "xyes"
 then
-	if test "x${ac_cv_header_unwind_h}" = "xyes"  -a "${UNWIND_LIBS}" != ""
+	if test "x${ac_cv_header_libunwind_h}" = "xyes"  -a "${UNWIND_LIBS}" != ""
 	then
 		AC_DEFINE([MOO_ENABLE_LIBUNWIND],[],[use libunwind for backtracing stack frames])
 	else
diff --git a/moo/lib/err.c b/moo/lib/err.c
index d3fc02a..7549b28 100644
--- a/moo/lib/err.c
+++ b/moo/lib/err.c
@@ -476,28 +476,28 @@ static void backtrace_stack_frames (moo_t* moo)
 {
 	unw_cursor_t cursor;
 	unw_context_t context;
+	int n;
 
 	unw_getcontext(&context);
 	unw_init_local(&cursor, &context);
 
-	int n=0;
-	while (unw_step(&cursor)) 
+	moo_logbfmt (moo, MOO_LOG_UNTYPED | MOO_LOG_DEBUG, "[BACKTRACE]\n");
+	for (n = 0; unw_step(&cursor) > 0; n++) 
 	{
 		unw_word_t ip, sp, off;
+		char symbol[256];
 
 		unw_get_reg (&cursor, UNW_REG_IP, &ip);
 		unw_get_reg (&cursor, UNW_REG_SP, &sp);
 
-		char symbol[256];
-
-		if (!unw_get_proc_name(&cursor, symbol, MOO_COUNTOF(symbol), &off)) 
+		if (unw_get_proc_name(&cursor, symbol, MOO_COUNTOF(symbol), &off)) 
 		{
-			moo_copy_bcstr (symbol, "<unknown>");
+			moo_copy_bcstr (symbol, MOO_COUNTOF(symbol), "<unknown>");
 		}
 
 		moo_logbfmt (moo, MOO_LOG_UNTYPED | MOO_LOG_DEBUG, 
-			"#%-2d 0x%016p p=0x%016p %s + 0x%zu\n", 
-			++n, (void*)ip, (void*)sp, symbol, (moo_oow_t)off);
+			"#%02d ip=0x%*p sp=0x%*p %s+0x%zu\n", 
+			n, MOO_SIZEOF(void*) * 2, (void*)ip, MOO_SIZEOF(void*) * 2, (void*)sp, symbol, (moo_oow_t)off);
 	}
 }
 #elif defined(HAVE_BACKTRACE)