diff --git a/include/mscomp/CircularBuffer.h b/include/mscomp/CircularBuffer.h
index 95ae27e..4638a64 100644
--- a/include/mscomp/CircularBuffer.h
+++ b/include/mscomp/CircularBuffer.h
@@ -39,6 +39,8 @@ class CircularBuffer
 		memcpy(this->buffer, rhs.buffer, Size);
 		this->tail = this->buffer + (rhs.tail - rhs.buffer);
 		this->full = rhs.full;
+
+		return *this;
 	}
 	INLINE bool empty() const { return UNLIKELY(!this->full && this->tail == this->buffer); }
 	INLINE uint32_t size() const { return LIKELY(this->full) ? Size : (uint32_t)(this->tail - this->buffer); }
diff --git a/include/mscomp/internal.h b/include/mscomp/internal.h
index 3bf4b45..8def5ad 100644
--- a/include/mscomp/internal.h
+++ b/include/mscomp/internal.h
@@ -454,16 +454,16 @@ typedef const_byte* RESTRICT const_rest_bytes;
 #endif
 
 #ifdef MSCOMP_WITH_ERROR_MESSAGES
-	#define SET_ERROR(s, ...)	snprintf(s->error, ARRAYSIZE(s->error), __VA_ARGS__)
-	#define INIT_STREAM_ERROR_MESSAGE(s) s->error[0] = 0
+	#define SET_ERROR(s, ...)	(s ? snprintf(s->error, ARRAYSIZE(s->error), __VA_ARGS__) : -1)
+	#define INIT_STREAM_ERROR_MESSAGE(s) (s ? s->error[0] = 0 : 0)
 #else
 	#define SET_ERROR(s, ...)
 	#define INIT_STREAM_ERROR_MESSAGE(s)
 #endif
 
 #ifdef MSCOMP_WITH_WARNING_MESSAGES
-	#define SET_WARNING(s, ...)	snprintf(s->warning, ARRAYSIZE(s->warning), __VA_ARGS__)
-	#define INIT_STREAM_WARNING_MESSAGE(s) s->warning[0] = 0
+	#define SET_WARNING(s, ...)	 (s ? snprintf(s->warning, ARRAYSIZE(s->warning), __VA_ARGS__) : -1)
+	#define INIT_STREAM_WARNING_MESSAGE(s) (s ? s->warning[0] = 0 : 0)
 #else
 	#define SET_WARNING(s, ...)
 	#define INIT_STREAM_WARNING_MESSAGE(s)