diff --git a/src/Makefile.am b/src/Makefile.am
index 56b8f48e746ccca9e1122d779464da0059ab2cb8..7c886448aa2cfa8dc3a060f6da14865df00f7ec0 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -52,7 +52,7 @@ include_HEADERS = space.h runner.h queue.h task.h lock.h cell.h part.h const.h \
     chemistry.h chemistry_io.h chemistry_struct.h cosmology.h restart.h space_getsid.h utilities.h \
     mesh_gravity.h cbrt.h exp10.h velociraptor_interface.h swift_velociraptor_part.h outputlist.h \
     logger_io.h tracers_io.h tracers.h tracers_struct.h star_formation_io.h fof.h fof_struct.h fof_io.h \
-    multipole.h multipole_struct.h \
+    multipole.h multipole_struct.h binomial.h \
     star_formation_struct.h star_formation.h star_formation_iact.h \
     star_formation_logger.h star_formation_logger_struct.h \
     pressure_floor.h pressure_floor_struct.h pressure_floor_iact.h \
diff --git a/src/binomial.h b/src/binomial.h
new file mode 100644
index 0000000000000000000000000000000000000000..24ea90e656a812aac2e2f8bfe7c64ace1af7e3b5
--- /dev/null
+++ b/src/binomial.h
@@ -0,0 +1,46 @@
+/*******************************************************************************
+ * This file is part of SWIFT.
+ * Copyright (c) 2020  Matthieu Schaller (schaller@strw.leidenuniv.nl)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ ******************************************************************************/
+#ifndef SWIFT_BINOMIAL_H
+#define SWIFT_BINOMIAL_H
+
+#include "error.h"
+#include "inline.h"
+
+/**
+ * @brief Compute the binomial coefficient (n, k)
+ *
+ * Only valid for values up to n = 5.
+ */
+__attribute__((const)) INLINE static int binomial(const int n, const int k) {
+
+#ifdef SWIFT_DEBUG_CHECKS
+  assert(n >= 0);
+  assert(k >= 0);
+  assert(n <= 5);
+  assert(k <= n);
+#endif
+
+  static const int coeffs[6][6] = {{1, 0, 0, 0, 0, 0}, {1, 1, 0, 0, 0, 0},
+                                   {1, 2, 1, 0, 0, 0}, {1, 3, 3, 1, 0, 0},
+                                   {1, 4, 6, 4, 1, 0}, {1, 5, 10, 10, 5, 1}};
+
+  return coeffs[n][k];
+}
+
+#endif /* SWIFT_BINOMIAL_H */
diff --git a/src/multipole.h b/src/multipole.h
index 79dde23d2df9955d246f08eaa880e7b2ee25b155..52e49417e2ba3eccf9015a9ca2b134f7d23e2767 100644
--- a/src/multipole.h
+++ b/src/multipole.h
@@ -30,6 +30,7 @@
 /* Includes. */
 #include "accumulate.h"
 #include "align.h"
+#include "binomial.h"
 #include "const.h"
 #include "error.h"
 #include "gravity.h"