diff --git a/mlir/include/mlir/CAPI/Utils.h b/mlir/include/mlir/CAPI/Utils.h
--- a/mlir/include/mlir/CAPI/Utils.h
+++ b/mlir/include/mlir/CAPI/Utils.h
@@ -28,7 +28,8 @@
 public:
   CallbackOstream(std::function<void(const char *, intptr_t, void *)> callback,
                   void *opaqueData)
-      : callback(callback), opaqueData(opaqueData), pos(0u) {}
+      : raw_ostream(/*unbuffered =*/true), callback(callback),
+        opaqueData(opaqueData), pos(0u) {}
 
   void write_impl(const char *ptr, size_t size) override {
     callback(ptr, size, opaqueData);
diff --git a/mlir/lib/CAPI/IR/AffineExpr.cpp b/mlir/lib/CAPI/IR/AffineExpr.cpp
--- a/mlir/lib/CAPI/IR/AffineExpr.cpp
+++ b/mlir/lib/CAPI/IR/AffineExpr.cpp
@@ -25,7 +25,6 @@
                          void *userData) {
   mlir::detail::CallbackOstream stream(callback, userData);
   unwrap(affineExpr).print(stream);
-  stream.flush();
 }
 
 void mlirAffineExprDump(MlirAffineExpr affineExpr) {
diff --git a/mlir/lib/CAPI/IR/AffineMap.cpp b/mlir/lib/CAPI/IR/AffineMap.cpp
--- a/mlir/lib/CAPI/IR/AffineMap.cpp
+++ b/mlir/lib/CAPI/IR/AffineMap.cpp
@@ -29,7 +29,6 @@
                         void *userData) {
   mlir::detail::CallbackOstream stream(callback, userData);
   unwrap(affineMap).print(stream);
-  stream.flush();
 }
 
 void mlirAffineMapDump(MlirAffineMap affineMap) { unwrap(affineMap).dump(); }
diff --git a/mlir/lib/CAPI/IR/Diagnostics.cpp b/mlir/lib/CAPI/IR/Diagnostics.cpp
--- a/mlir/lib/CAPI/IR/Diagnostics.cpp
+++ b/mlir/lib/CAPI/IR/Diagnostics.cpp
@@ -19,7 +19,6 @@
                          void *userData) {
   detail::CallbackOstream stream(callback, userData);
   unwrap(diagnostic).print(stream);
-  stream.flush();
 }
 
 MlirLocation mlirDiagnosticGetLocation(MlirDiagnostic diagnostic) {
diff --git a/mlir/lib/CAPI/IR/IR.cpp b/mlir/lib/CAPI/IR/IR.cpp
--- a/mlir/lib/CAPI/IR/IR.cpp
+++ b/mlir/lib/CAPI/IR/IR.cpp
@@ -126,7 +126,6 @@
                        void *userData) {
   detail::CallbackOstream stream(callback, userData);
   unwrap(location).print(stream);
-  stream.flush();
 }
 
 /* ========================================================================== */
@@ -325,14 +324,12 @@
                         void *userData) {
   detail::CallbackOstream stream(callback, userData);
   unwrap(op)->print(stream);
-  stream.flush();
 }
 
 void mlirOperationPrintWithFlags(MlirOperation op, MlirOpPrintingFlags flags,
                                  MlirStringCallback callback, void *userData) {
   detail::CallbackOstream stream(callback, userData);
   unwrap(op)->print(stream, *unwrap(flags));
-  stream.flush();
 }
 
 void mlirOperationDump(MlirOperation op) { return unwrap(op)->dump(); }
@@ -476,7 +473,6 @@
                     void *userData) {
   detail::CallbackOstream stream(callback, userData);
   unwrap(block)->print(stream);
-  stream.flush();
 }
 
 /* ========================================================================== */
@@ -523,7 +519,6 @@
                     void *userData) {
   detail::CallbackOstream stream(callback, userData);
   unwrap(value).print(stream);
-  stream.flush();
 }
 
 /* ========================================================================== */
@@ -543,7 +538,6 @@
 void mlirTypePrint(MlirType type, MlirStringCallback callback, void *userData) {
   detail::CallbackOstream stream(callback, userData);
   unwrap(type).print(stream);
-  stream.flush();
 }
 
 void mlirTypeDump(MlirType type) { unwrap(type).dump(); }
@@ -572,7 +566,6 @@
                         void *userData) {
   detail::CallbackOstream stream(callback, userData);
   unwrap(attr).print(stream);
-  stream.flush();
 }
 
 void mlirAttributeDump(MlirAttribute attr) { unwrap(attr).dump(); }