diff --git a/src/spectrum/model/spectrum-value.h b/src/spectrum/model/spectrum-value.h
index a6fd3188a..5d5594575 100644
--- a/src/spectrum/model/spectrum-value.h
+++ b/src/spectrum/model/spectrum-value.h
@@ -540,6 +540,7 @@ SpectrumValue Pow (double base, const SpectrumValue& exp);
 SpectrumValue Log10 (const SpectrumValue&  arg);
 SpectrumValue Log2 (const SpectrumValue&  arg);
 SpectrumValue Log (const SpectrumValue&  arg);
+double Integral (const SpectrumValue& x);
 
 
 } // namespace ns3