diff --git a/flang/runtime/io-stmt.cpp b/flang/runtime/io-stmt.cpp
index 4072dbf265944..398f6127cf275 100644
--- a/flang/runtime/io-stmt.cpp
+++ b/flang/runtime/io-stmt.cpp
@@ -1219,6 +1219,7 @@ bool InquireUnitState::Inquire(
   case HashInquiryKeyword("SIZE"):
     result = -1;
     if (unit().IsConnected()) {
+      unit().FlushOutput(*this);
       if (auto size{unit().knownSize()}) {
         result = *size;
       }