diff --git a/src/core/p3m/interpolation.hpp b/src/core/p3m/interpolation.hpp
index a25b0d8f66..0573648938 100644
--- a/src/core/p3m/interpolation.hpp
+++ b/src/core/p3m/interpolation.hpp
@@ -109,10 +109,10 @@ class p3m_interpolation_cache {
     InterpolationWeights<cao> ret;
     ret.ind = ca_fmp[i];
 
-    auto const offset = ca_frac.data() + 3 * i * m_cao;
-    boost::copy(make_const_span(offset + 0 * m_cao, m_cao), ret.w_x.begin());
-    boost::copy(make_const_span(offset + 1 * m_cao, m_cao), ret.w_y.begin());
-    boost::copy(make_const_span(offset + 2 * m_cao, m_cao), ret.w_z.begin());
+    auto const offset = ca_frac.data() + 3 * i * cao;
+    boost::copy(make_const_span(offset + 0 * cao, cao), ret.w_x.begin());
+    boost::copy(make_const_span(offset + 1 * cao, cao), ret.w_y.begin());
+    boost::copy(make_const_span(offset + 2 * cao, cao), ret.w_z.begin());
 
     return ret;
   }