diff --git a/lib/potential/gm_data.cpp b/lib/potential/gm_data.cpp
index 091c9b0..3ce865e 100644
--- a/lib/potential/gm_data.cpp
+++ b/lib/potential/gm_data.cpp
@@ -357,7 +357,7 @@ void gctl::power_spectrum(array<double> &P, const array<double> &C, const array<
             P[i - n] += (C[id + j]*C[id + j] + S[id + j]*S[id + j]);
         }
 
-        P[i - n] *= (n + 1)*pow(R/r, 2*n + 4);
+        P[i - n] *= (i + 1)*pow(R/r, 2*i + 4);
     }
     return;
 }
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