diff --git a/CHANGELOG.md b/CHANGELOG.md
index d233d0196..c198c525f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 ### Changed
 - Automatically detect VLLEs in `BinaryPhaseDiagram`. [#341](https://github.com/feos-org/feos/pull/341)
+- Correct missing minus sign for `isothermal_compressibility`. [#342](https://github.com/feos-org/feos/pull/342)
 
 ## [0.9.3] - 2026-01-26
 ### Added
diff --git a/crates/feos-core/src/state/residual_properties.rs b/crates/feos-core/src/state/residual_properties.rs
index 179ff6d19..554facf08 100644
--- a/crates/feos-core/src/state/residual_properties.rs
+++ b/crates/feos-core/src/state/residual_properties.rs
@@ -272,7 +272,7 @@ where
 
     /// Isothermal compressibility: $\kappa_T=-\frac{1}{V}\left(\frac{\partial V}{\partial p}\right)_{T,N_i}$
     pub fn isothermal_compressibility(&self) -> InvP<D> {
-        (self.dp_dv(Contributions::Total) * self.volume).inv()
+        -(self.dp_dv(Contributions::Total) * self.volume).inv()
     }
 
     // entropy derivatives