diff --git a/feos-core/CHANGELOG.md b/feos-core/CHANGELOG.md
index e12e758b1..33c06cafe 100644
--- a/feos-core/CHANGELOG.md
+++ b/feos-core/CHANGELOG.md
@@ -5,6 +5,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## Unreleased
+### Fixed
+- Avoid panicking when calculating `ResidualNpt` properties of states with negative pressures. [#42](https://github.com/feos-org/feos/pull/42)
 
 ## [0.3.0] - 2022-06-13
 ### Added
diff --git a/feos-core/src/state/mod.rs b/feos-core/src/state/mod.rs
index 86678f528..8baad3097 100644
--- a/feos-core/src/state/mod.rs
+++ b/feos-core/src/state/mod.rs
@@ -232,16 +232,25 @@ impl<U: EosUnit, E: EquationOfState> State<U, E> {
         eos.validate_moles(Some(moles))?;
         validate(temperature, volume, moles)?;
 
-        let t = temperature.to_reduced(U::reference_temperature())?;
-        let v = volume.to_reduced(U::reference_volume())?;
-        let m = moles.to_reduced(U::reference_moles())?;
+        Ok(Self::new_nvt_unchecked(eos, temperature, volume, moles))
+    }
+
+    pub(super) fn new_nvt_unchecked(
+        eos: &Rc<E>,
+        temperature: QuantityScalar<U>,
+        volume: QuantityScalar<U>,
+        moles: &QuantityArray1<U>,
+    ) -> Self {
+        let t = temperature.to_reduced(U::reference_temperature()).unwrap();
+        let v = volume.to_reduced(U::reference_volume()).unwrap();
+        let m = moles.to_reduced(U::reference_moles()).unwrap();
 
         let total_moles = moles.sum();
         let partial_density = moles / volume;
         let density = total_moles / volume;
-        let molefracs = &m / total_moles.to_reduced(U::reference_moles())?;
+        let molefracs = &m / total_moles.to_reduced(U::reference_moles()).unwrap();
 
-        Ok(State {
+        State {
             eos: eos.clone(),
             total_moles,
             temperature,
@@ -254,7 +263,7 @@ impl<U: EosUnit, E: EquationOfState> State<U, E> {
             reduced_volume: v,
             reduced_moles: m,
             cache: RefCell::new(Cache::with_capacity(eos.components())),
-        })
+        }
     }
 
     /// Return a new `State` for a pure component given a temperature and a density. The moles
diff --git a/feos-core/src/state/properties.rs b/feos-core/src/state/properties.rs
index 5e0289765..13d0ea400 100644
--- a/feos-core/src/state/properties.rs
+++ b/feos-core/src/state/properties.rs
@@ -155,13 +155,12 @@ impl<U: EosUnit, E: EquationOfState> State<U, E> {
             }
             Contributions::ResidualNpt => {
                 let p = self.pressure_(Evaluate::Total);
-                let state_p = Self::new_nvt(
+                let state_p = Self::new_nvt_unchecked(
                     &self.eos,
                     self.temperature,
                     self.total_moles * U::gas_constant() * self.temperature / p,
                     &self.moles,
-                )
-                .unwrap();
+                );
                 if additive {
                     f(self, Evaluate::Residual) + f(self, Evaluate::IdealGasDelta)
                         - f(&state_p, Evaluate::IdealGasDelta)