diff --git a/spectrogram.cpp b/spectrogram.cpp
index 90255c1..36c95b6 100644
--- a/spectrogram.cpp
+++ b/spectrogram.cpp
@@ -97,7 +97,7 @@ void Spectrogram::paintEvent(QPaintEvent *event)
 
 float* Spectrogram::getTile(off_t tile)
 {
-	float *obj = fftCache.object(qMakePair(fftSize, tile));
+	float *obj = fftCache.object(TileCacheKey(fftSize, zoomLevel, tile));
 	if (obj != 0)
 		return obj;
 
@@ -109,7 +109,7 @@ float* Spectrogram::getTile(off_t tile)
 		sample += getStride();
 		ptr += fftSize;
 	}
-	fftCache.insert(qMakePair(fftSize, tile), dest);
+	fftCache.insert(TileCacheKey(fftSize, zoomLevel, tile), dest);
 	return dest;
 }
 
@@ -222,3 +222,7 @@ QString Spectrogram::sampleToTime(off_t sample)
 int Spectrogram::linesPerTile() {
 	return tileSize / fftSize;
 }
+
+uint qHash(const TileCacheKey &key, uint seed) {
+	return key.fftSize ^ key.zoomLevel ^ key.sample ^ seed;
+}
diff --git a/spectrogram.h b/spectrogram.h
index cf748a2..190e4d4 100644
--- a/spectrogram.h
+++ b/spectrogram.h
@@ -9,6 +9,8 @@
 
 static const double Tau = M_PI * 2.0;
 
+class TileCacheKey;
+
 class Spectrogram : public QWidget {
 	Q_OBJECT
 
@@ -39,7 +41,7 @@ private:
 	FFT *fft = nullptr;
 	std::unique_ptr<float[]> window;
 	fftwf_complex *lineBuffer = nullptr;
-	QCache<QPair<int, off_t>, float> fftCache;
+	QCache<TileCacheKey, float> fftCache;
 	uint colormap[256];
 
 	int sampleRate;
@@ -55,4 +57,24 @@ private:
 	int sampleToLine(off_t sample);
 	QString sampleToTime(off_t sample);
 	int linesPerTile();
-};
\ No newline at end of file
+};
+
+class TileCacheKey {
+
+public:
+	TileCacheKey(int fftSize, int zoomLevel, off_t sample) {
+		this->fftSize = fftSize;
+		this->zoomLevel = zoomLevel;
+		this->sample = sample;
+	}
+
+	bool operator==(const TileCacheKey &k2) const {
+		return (this->fftSize == k2.fftSize) &&
+				(this->zoomLevel == k2.zoomLevel) &&
+				(this->sample == k2.sample);
+	}
+
+	int fftSize;
+	int zoomLevel;
+	off_t sample;
+};