diff --git a/src/thermophysicalModels/specie/equationOfState/incompressiblePerfectGas/incompressiblePerfectGas.H b/src/thermophysicalModels/specie/equationOfState/incompressiblePerfectGas/incompressiblePerfectGas.H
index a752cc924a042eb78d44ba99b3fec16e122e3474..fd4e2d6d3688e4d446fae65406e6a00af68d10ff 100644
--- a/src/thermophysicalModels/specie/equationOfState/incompressiblePerfectGas/incompressiblePerfectGas.H
+++ b/src/thermophysicalModels/specie/equationOfState/incompressiblePerfectGas/incompressiblePerfectGas.H
@@ -172,25 +172,25 @@ public:
 
     // Friend operators
 
-        inline friend incompressiblePerfectGas operator+ <Specie>
+        friend incompressiblePerfectGas operator+ <Specie>
         (
             const incompressiblePerfectGas&,
             const incompressiblePerfectGas&
         );
 
-        inline friend incompressiblePerfectGas operator- <Specie>
+        friend incompressiblePerfectGas operator- <Specie>
         (
             const incompressiblePerfectGas&,
             const incompressiblePerfectGas&
         );
 
-        inline friend incompressiblePerfectGas operator* <Specie>
+        friend incompressiblePerfectGas operator* <Specie>
         (
             const scalar s,
             const incompressiblePerfectGas&
         );
 
-        inline friend incompressiblePerfectGas operator== <Specie>
+        friend incompressiblePerfectGas operator== <Specie>
         (
             const incompressiblePerfectGas&,
             const incompressiblePerfectGas&
diff --git a/src/thermophysicalModels/specie/equationOfState/perfectGas/perfectGas.H b/src/thermophysicalModels/specie/equationOfState/perfectGas/perfectGas.H
index a0cff64517e7a484dffa5e9c179a53897e145fce..4b02137b257eb70e9c82142323bd8502095eb490 100644
--- a/src/thermophysicalModels/specie/equationOfState/perfectGas/perfectGas.H
+++ b/src/thermophysicalModels/specie/equationOfState/perfectGas/perfectGas.H
@@ -158,25 +158,25 @@ public:
 
     // Friend operators
 
-        inline friend perfectGas operator+ <Specie>
+        friend perfectGas operator+ <Specie>
         (
             const perfectGas&,
             const perfectGas&
         );
 
-        inline friend perfectGas operator- <Specie>
+        friend perfectGas operator- <Specie>
         (
             const perfectGas&,
             const perfectGas&
         );
 
-        inline friend perfectGas operator* <Specie>
+        friend perfectGas operator* <Specie>
         (
             const scalar s,
             const perfectGas&
         );
 
-        inline friend perfectGas operator== <Specie>
+        friend perfectGas operator== <Specie>
         (
             const perfectGas&,
             const perfectGas&
diff --git a/src/thermophysicalModels/specie/equationOfState/rhoConst/rhoConst.H b/src/thermophysicalModels/specie/equationOfState/rhoConst/rhoConst.H
index af4af4adbd8e767fe0fd206048bead4272b0075b..5eccbbc233bb953216f9de316a4e52b87c1f7e27 100644
--- a/src/thermophysicalModels/specie/equationOfState/rhoConst/rhoConst.H
+++ b/src/thermophysicalModels/specie/equationOfState/rhoConst/rhoConst.H
@@ -160,25 +160,25 @@ public:
 
     // Friend operators
 
-        inline friend rhoConst operator+ <Specie>
+        friend rhoConst operator+ <Specie>
         (
             const rhoConst&,
             const rhoConst&
         );
 
-        inline friend rhoConst operator- <Specie>
+        friend rhoConst operator- <Specie>
         (
             const rhoConst&,
             const rhoConst&
         );
 
-        inline friend rhoConst operator* <Specie>
+        friend rhoConst operator* <Specie>
         (
             const scalar s,
             const rhoConst&
         );
 
-        inline friend rhoConst operator== <Specie>
+        friend rhoConst operator== <Specie>
         (
             const rhoConst&,
             const rhoConst&