diff --git a/demboyz/demofile.cpp b/demboyz/demofile.cpp
index f0e75dc..091fb3c 100644
--- a/demboyz/demofile.cpp
+++ b/demboyz/demofile.cpp
@@ -2,6 +2,7 @@
 #include "demofile.h"
 #include "demotypes.h"
 #include <cassert>
+#include <utility>
 
 // DemoFileReader
 
@@ -10,6 +11,11 @@ DemoFileReader::DemoFileReader(FILE* fp):
 {
 }
 
+bool DemoFileReader::IsOk() const
+{
+    return ferror(m_demoFp) == 0;
+}
+
 void DemoFileReader::ReadDemoHeader(demoheader_t& header)
 {
     fread(&header, sizeof(demoheader_t), 1, m_demoFp);
@@ -102,6 +108,11 @@ DemoFileWriter::DemoFileWriter(FILE* fp) :
 {
 }
 
+bool DemoFileWriter::IsOk() const
+{
+    return ferror(m_demoFp) == 0;
+}
+
 void DemoFileWriter::WriteDemoHeader(const demoheader_t& header)
 {
     fwrite(&header, sizeof(demoheader_t), 1, m_demoFp);
diff --git a/demboyz/demofile.h b/demboyz/demofile.h
index d5985af..77e36a2 100644
--- a/demboyz/demofile.h
+++ b/demboyz/demofile.h
@@ -13,6 +13,7 @@ class DemoFileReader
 public:
     DemoFileReader(FILE* fp);
 
+    bool IsOk() const;
     void ReadDemoHeader(demoheader_t& header);
     int32_t ReadRawData(uint8_t* buffer, int32_t maxLength);
     Array<uint8_t> ReadRawData(int32_t maxLength);
@@ -31,6 +32,7 @@ class DemoFileWriter
 public:
     DemoFileWriter(FILE* fp);
 
+    bool IsOk() const;
     void WriteDemoHeader(const demoheader_t& header);
     void WriteRawData(const uint8_t* buffer, int32_t length);
     void WriteSequenceInfo(int32_t seqNum1, int32_t seqNum2);