diff --git a/dumux/material/fluidsystems/1padapter.hh b/dumux/material/fluidsystems/1padapter.hh
index d023684d7e4d8447be3c17633039c60478d285a0..a7e4f40d27e04cab47948ab03107dc57f3f1d56c 100644
--- a/dumux/material/fluidsystems/1padapter.hh
+++ b/dumux/material/fluidsystems/1padapter.hh
@@ -60,7 +60,9 @@ class OnePAdapter
                 DUNE_THROW(Dune::InvalidStateException, "Only phase " << phase << " is available!");
         }
 
-        // the main component has to be index 0 so we swap the main component with the first component
+        // the main component is currently excepted to have the same index as it's phase
+        // (see Fluidsystems::Base::getMainComponent for more information)
+        // so we swap the main component with the first component
         // this mapping works in both ways since we are only swapping components
         static constexpr int compIdx(int compIdx)
         {
diff --git a/dumux/material/fluidsystems/base.hh b/dumux/material/fluidsystems/base.hh
index fbc36961cf7272613c8d57873f2c0994e87e81c3..0768dfc6a7be0bee62a366a906cdc446c819af1e 100644
--- a/dumux/material/fluidsystems/base.hh
+++ b/dumux/material/fluidsystems/base.hh
@@ -60,8 +60,11 @@ public:
      * \brief Get the main component of a given phase if possible
      *
      * \param phaseIdx The index of the fluid phase to consider
-     * \note This method has to can throw at compile time if the fluid system doesn't assume a
+     * \note This method has to can assert at compile time if the fluid system doesn't assume a
      *       main phase. Then using e.g. Fick's law will fail compiling.
+     * \todo Unfortunately we currently still have the assumption in some volume variables (e.g. 1pnc, 2pnc)
+     *       that the main component index of a phase is equal to the phase index of that phase. This means
+     *       changing this only works if the volume variables are written accordingly.
      */
     static constexpr int getMainComponent(int phaseIdx)
     { return phaseIdx; }