diff --git a/RtAudio.cpp b/RtAudio.cpp
index ddb423a..1d23516 100644
--- a/RtAudio.cpp
+++ b/RtAudio.cpp
@@ -4977,7 +4977,8 @@ void RtApiWasapi::wasapiThread()
   }
 
   if ( stream_.mode == INPUT ) {
-    convBuffSize = ( size_t ) ( stream_.bufferSize * captureSrRatio ) * stream_.nDeviceChannels[INPUT] * formatBytes( stream_.deviceFormat[INPUT] );
+    using namespace std; // for roundf
+    convBuffSize = ( size_t ) roundf( stream_.bufferSize * captureSrRatio ) * stream_.nDeviceChannels[INPUT] * formatBytes( stream_.deviceFormat[INPUT] );
     deviceBuffSize = stream_.bufferSize * stream_.nDeviceChannels[INPUT] * formatBytes( stream_.deviceFormat[INPUT] );
   }
   else if ( stream_.mode == OUTPUT ) {