diff --git a/src/Makefile.am b/src/Makefile.am
index 3b78a428f608c55d2009e15b90e19b2dab6a4161..8693a23fcb37985ba01bdcac811155137ddadeac 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -54,11 +54,11 @@ AM_SOURCES = space.c runner.c queue.c task.c cell.c engine.c \
 # Include files for distribution, not installation.
 nobase_noinst_HEADERS = approx_math.h atomic.h cycle.h error.h inline.h kernel_hydro.h kernel_gravity.h \
 		 vector.h runner_doiact.h runner_doiact_grav.h units.h intrinsics.h minmax.h kick.h \
-		 timestep.h drift.h \
+		 timestep.h drift.h adiabatic_index.h \
 		 gravity.h gravity_io.h \
 		 gravity/Default/gravity.h gravity/Default/gravity_iact.h gravity/Default/gravity_io.h \
 		 gravity/Default/gravity_debug.h gravity/Default/gravity_part.h  \
-	 	 hydro.h hydro_io.h gamma.h \
+                 hydro.h hydro_io.h \
 		 hydro/Minimal/hydro.h hydro/Minimal/hydro_iact.h hydro/Minimal/hydro_io.h \
                  hydro/Minimal/hydro_debug.h hydro/Minimal/hydro_part.h \
 		 hydro/Default/hydro.h hydro/Default/hydro_iact.h hydro/Default/hydro_io.h \
diff --git a/src/gamma.h b/src/adiabatic_index.h
similarity index 100%
rename from src/gamma.h
rename to src/adiabatic_index.h
diff --git a/src/hydro/Default/hydro.h b/src/hydro/Default/hydro.h
index a670515381a5fce6bcd524bc12e72f28d597687d..a09920235eedcc6c997c1407d7f6c63d8f7a630f 100644
--- a/src/hydro/Default/hydro.h
+++ b/src/hydro/Default/hydro.h
@@ -17,8 +17,8 @@
  *
  ******************************************************************************/
 
+#include "adiabatic_index.h"
 #include "approx_math.h"
-#include "gamma.h"
 
 /**
  * @brief Computes the hydro time-step of a given particle
diff --git a/src/hydro/Gadget2/hydro.h b/src/hydro/Gadget2/hydro.h
index 4081679d4980fd158c14906cc79073e2b6956c33..d0ca5817dda1243957ad1b28c13cee18ab9aea21 100644
--- a/src/hydro/Gadget2/hydro.h
+++ b/src/hydro/Gadget2/hydro.h
@@ -17,7 +17,7 @@
  *
  ******************************************************************************/
 
-#include "gamma.h"
+#include "adiabatic_index.h"
 
 /**
  * @brief Computes the hydro time-step of a given particle
diff --git a/src/hydro_properties.c b/src/hydro_properties.c
index 756b9958b78bc9366687d5e183759ec22b587bdc..ec0c6113fe9900adcbf05f084cb4a0bd33e6cdf3 100644
--- a/src/hydro_properties.c
+++ b/src/hydro_properties.c
@@ -25,9 +25,9 @@
 #include <math.h>
 
 /* Local headers. */
+#include "adiabatic_index.h"
 #include "common_io.h"
 #include "error.h"
-#include "gamma.h"
 #include "hydro.h"
 #include "kernel_hydro.h"
 
diff --git a/src/units.c b/src/units.c
index ca75fc7ee6c66dbcd5cc7fd5e53d2c881c43ec68..dd9576adc4bb18b859cff03c674f31b721409a19 100644
--- a/src/units.c
+++ b/src/units.c
@@ -37,9 +37,9 @@
 #include "units.h"
 
 /* Includes. */
+#include "adiabatic_index.h"
 #include "const.h"
 #include "error.h"
-#include "gamma.h"
 
 /**
  * @brief Initialises the UnitSystem structure with the constants given in