3 files changed, 17 insertions, 2 deletions
diff --git a/flang-rt/include/flang-rt/runtime/environment.h b/flang-rt/include/flang-rt/runtime/environment.h
index b91cf629509a..72157fe4418e 100644
--- a/flang-rt/include/flang-rt/runtime/environment.h
+++ b/flang-rt/include/flang-rt/runtime/environment.h
@@ -73,6 +73,7 @@ struct ExecutionEnvironment {
   bool noStopMessage{false}; // NO_STOP_MESSAGE=1 inhibits "Fortran STOP"
   bool defaultUTF8{false}; // DEFAULT_UTF8
   bool checkPointerDeallocation{true}; // FORT_CHECK_POINTER_DEALLOCATION
+  bool truncateStream{true}; // FORT_TRUNCATE_STREAM
 
   enum InternalDebugging { WorkQueue = 1 };
   int internalDebugging{0}; // FLANG_RT_DEBUG
diff --git a/flang-rt/lib/runtime/environment.cpp b/flang-rt/lib/runtime/environment.cpp
index 2a2e19f9f17e..be4f7308ab02 100644
--- a/flang-rt/lib/runtime/environment.cpp
+++ b/flang-rt/lib/runtime/environment.cpp
@@ -141,6 +141,17 @@ void ExecutionEnvironment::Configure(int ac, const char *av[],
     }
   }
 
+  if (auto *x{std::getenv("FORT_TRUNCATE_STREAM")}) {
+    char *end;
+    auto n{std::strtol(x, &end, 10)};
+    if (n >= 0 && n <= 1 && *end == '\0') {
+      truncateStream = n != 0;
+    } else {
+      std::fprintf(stderr,
+          "Fortran runtime: FORT_TRUNCATE_STREAM=%s is invalid; ignored\n", x);
+    }
+  }
+
   if (auto *x{std::getenv("NO_STOP_MESSAGE")}) {
     char *end;
     auto n{std::strtol(x, &end, 10)};
diff --git a/flang-rt/lib/runtime/unit.cpp b/flang-rt/lib/runtime/unit.cpp
index 549fbeaca05b..bc98cfdcbe5d 100644
--- a/flang-rt/lib/runtime/unit.cpp
+++ b/flang-rt/lib/runtime/unit.cpp
@@ -783,8 +783,11 @@ void ExternalFileUnit::DoEndfile(IoErrorHandler &handler) {
   frameOffsetInFile_ += recordOffsetInFrame_ + furthestPositionInRecord;
   recordOffsetInFrame_ = 0;
   FlushOutput(handler);
-  Truncate(frameOffsetInFile_, handler);
-  TruncateFrame(frameOffsetInFile_, handler);
+  if (access != Access::Stream || executionEnvironment.truncateStream) {
+    // Stream output after positioning truncates with some compilers.
+    Truncate(frameOffsetInFile_, handler);
+    TruncateFrame(frameOffsetInFile_, handler);
+  }
   BeginRecord();
   impliedEndfile_ = false;
   anyWriteSinceLastPositioning_ = false;