diff --git a/inc/winfsp/fsctl.h b/inc/winfsp/fsctl.h
index facd8b46..7a957a5c 100644
--- a/inc/winfsp/fsctl.h
+++ b/inc/winfsp/fsctl.h
@@ -30,7 +30,9 @@ extern const __declspec(selectany) GUID FspFsvrtDeviceClassGuid =
     CTL_CODE(FILE_DEVICE_FILE_SYSTEM, 0x800 + 'T', METHOD_BUFFERED, FILE_ANY_ACCESS)
 
 #define FSP_FSCTL_CREATE_BUFFER_SIZE    128
-#define FSP_FSCTL_TRANSACT_BUFFER_SIZE  4096
+#define FSP_FSCTL_TRANSACT_BUFFER_SIZE  (16 * 1024)
+#define FSP_FSCTL_TRANSACT_REQ_SIZEMAX  (sizeof(FSP_TRANSACT_REQ) + 1024 * sizeof(WCHAR))
+#define FSP_FSCTL_TRANSACT_RSP_SIZEMAX  (sizeof(FSP_TRANSACT_RSP) + 1024 * sizeof(WCHAR))
 
 /* marshalling */
 #pragma warning(push)
diff --git a/src/sys/fsctl.c b/src/sys/fsctl.c
index 6f67d892..a6d96d0f 100644
--- a/src/sys/fsctl.c
+++ b/src/sys/fsctl.c
@@ -186,6 +186,10 @@ static NTSTATUS FspFsvrtTransact(
             return STATUS_CANCELLED;
         }
 
+        /* check that we have enough space before pulling the next pending IRP off the queue */
+        if ((PUINT8)Request + FSP_FSCTL_TRANSACT_REQ_SIZEMAX > SystemBufferEnd)
+            break;
+
         PendingIrp = FspIoqNextPendingIrp(&FsvrtDeviceExtension->Ioq, 0);
         if (0 == PendingIrp)
             break;