diff --git a/var/spack/repos/builtin/packages/namd/package.py b/var/spack/repos/builtin/packages/namd/package.py
index 496f9f52c40108fb46e2d7d28ca8a1cb443bff35..d335a2c631767323c9f2bb0302f72104bc8c1cd8 100644
--- a/var/spack/repos/builtin/packages/namd/package.py
+++ b/var/spack/repos/builtin/packages/namd/package.py
@@ -92,7 +92,7 @@ def edit(self, spec, prefix):
 
         self._copy_arch_file('base')
 
-        opts = ['--charm-base', spec['charm'].prefix]
+        opts = ['--charm-base', spec['charmpp'].prefix]
         fftw_version = spec.variants['fftw'].value
         if fftw_version == 'none':
             opts.append('--without-fftw')