diff --git a/moo/lib/exec.c b/moo/lib/exec.c
index 1b2c7e8..a3b9920 100644
--- a/moo/lib/exec.c
+++ b/moo/lib/exec.c
@@ -5305,11 +5305,11 @@ static int __execute (moo_t* moo)
 			/* it emulates thisContext blockCopy: nargs ofTmprCount: ntmprs */
 			MOO_ASSERT (moo, moo->sp >= 2);
 
-			MOO_ASSERT (moo, MOO_CLASSOF(moo, MOO_STACK_GETTOP(moo)) == moo->_small_integer);
+			MOO_ASSERT (moo, MOO_OOP_IS_SMOOI(MOO_STACK_GETTOP(moo)));
 			ntmprs = MOO_OOP_TO_SMOOI(MOO_STACK_GETTOP(moo));
 			MOO_STACK_POP (moo);
 
-			MOO_ASSERT (moo, MOO_CLASSOF(moo, MOO_STACK_GETTOP(moo)) == moo->_small_integer);
+			MOO_ASSERT (moo, MOO_OOP_IS_SMOOI(MOO_STACK_GETTOP(moo)));
 			nargs = MOO_OOP_TO_SMOOI(MOO_STACK_GETTOP(moo));
 			MOO_STACK_POP (moo);
 
diff --git a/moo/lib/logfmtv.h b/moo/lib/logfmtv.h
index b5c4cfd..35079d7 100644
--- a/moo/lib/logfmtv.h
+++ b/moo/lib/logfmtv.h
@@ -73,16 +73,20 @@
 
 #define PUT_OOCH(c,n) do { \
 	int xx; \
-	if ((xx = data->putch (moo, data->mask, c, n)) <= -1) goto oops; \
-	if (xx == 0) goto done; \
-	data->count += n; \
+	if (n > 0) { \
+		if ((xx = data->putch (moo, data->mask, c, n)) <= -1) goto oops; \
+		if (xx == 0) goto done; \
+		data->count += n; \
+	} \
 } while (0)
 
 #define PUT_OOCS(ptr,len) do { \
 	int xx; \
-	if ((xx = data->putcs (moo, data->mask, ptr, len)) <= -1) goto oops; \
-	if (xx == 0) goto done; \
-	data->count += len; \
+	if (len > 0) { \
+		if ((xx = data->putcs (moo, data->mask, ptr, len)) <= -1) goto oops; \
+		if (xx == 0) goto done; \
+		data->count += len; \
+	} \
 } while (0)
 
 static int logfmtv (moo_t* moo, const fmtchar_t* fmt, moo_fmtout_t* data, va_list ap, outbfmt_t outbfmt)