Index: src/OFStream.h
==================================================================
--- src/OFStream.h
+++ src/OFStream.h
@@ -965,12 +965,16 @@
 - (nullable OFString *)tryReadTillDelimiter: (OFString *)delimiter
 				   encoding: (OFStringEncoding)encoding;
 
 /**
  * @brief Writes everything in the write buffer to the stream.
+ *
+ * @return Whether the write buffer was flushed entirely. On non-blocking
+ *	   sockets, this can return `false` if flushing the write buffer in its
+ *	   entirety would block.
  */
-- (void)flushWriteBuffer;
+- (bool)flushWriteBuffer;
 
 /**
  * @brief Writes from a buffer into the stream.
  *
  * In non-blocking mode, if less than the specified length could be written, an

Index: src/OFStream.m
==================================================================
--- src/OFStream.m
+++ src/OFStream.m
@@ -1054,27 +1054,29 @@
 {
 	return [self tryReadTillDelimiter: delimiter
 				 encoding: OFStringEncodingUTF8];
 }
 
-- (void)flushWriteBuffer
+- (bool)flushWriteBuffer
 {
 	size_t bytesWritten;
 
 	if (_writeBuffer == NULL)
-		return;
+		return true;
 
 	bytesWritten = [self lowlevelWriteBuffer: _writeBuffer
 					  length: _writeBufferLength];
 
 	if (bytesWritten == 0)
-		return;
+		return false;
 
 	if (bytesWritten == _writeBufferLength) {
 		OFFreeMemory(_writeBuffer);
 		_writeBuffer = NULL;
 		_writeBufferLength = 0;
+
+		return true;
 	}
 
 	OFEnsure(bytesWritten <= _writeBufferLength);
 
 	memmove(_writeBuffer, _writeBuffer + bytesWritten,
@@ -1084,10 +1086,12 @@
 		_writeBuffer = OFResizeMemory(_writeBuffer,
 		    _writeBufferLength, 1);
 	} @catch (OFOutOfMemoryException *e) {
 		/* We don't care, as we only made it smaller. */
 	}
+
+	return false;
 }
 
 - (void)writeBuffer: (const void *)buffer length: (size_t)length
 {
 	if (!_buffersWrites) {