diff --git a/src/schreier-sims.c b/src/schreier-sims.c
index 6961a83c5..776c1920e 100644
--- a/src/schreier-sims.c
+++ b/src/schreier-sims.c
@@ -25,7 +25,7 @@ uint16_t PERM_DEGREE = 0;
 
 // Schreier-Sims set up
 
-SchreierSims* new_schreier_sims() {
+SchreierSims* new_schreier_sims(void) {
   SchreierSims* ss = malloc(sizeof(SchreierSims));
   ss->tmp_perm     = new_perm(MAXVERTS);
   for (uint16_t i = 0; i < MAXVERTS; ++i) {
diff --git a/src/schreier-sims.h b/src/schreier-sims.h
index 6385746c6..55e563475 100644
--- a/src/schreier-sims.h
+++ b/src/schreier-sims.h
@@ -39,7 +39,7 @@ struct schreier_sims_struct {
 
 typedef struct schreier_sims_struct SchreierSims;
 
-SchreierSims* new_schreier_sims();
+SchreierSims* new_schreier_sims(void);
 
 // Store the stabiliser of pt in the group generated by src, in dst, use ss to
 // hold the stabiliser chain.