diff --git a/iseq.c b/iseq.c
index 68ca781d4c..935c69d434 100644
--- a/iseq.c
+++ b/iseq.c
@@ -980,7 +980,7 @@ remove_coverage_i(void *vstart, void *vend, size_t stride, void *data)
 }
 
 void
-rb_iseq_remove_coverage_all()
+rb_iseq_remove_coverage_all(void)
 {
     rb_objspace_each_objects(remove_coverage_i, NULL);
 }
diff --git a/iseq.h b/iseq.h
index 44ed3bdedf..2062c33bb4 100644
--- a/iseq.h
+++ b/iseq.h
@@ -178,7 +178,7 @@ VALUE rb_iseq_first_lineno(const rb_iseq_t *iseq);
 VALUE rb_iseq_method_name(const rb_iseq_t *iseq);
 void rb_iseq_code_location(const rb_iseq_t *iseq, int *first_lineno, int *first_column, int *last_lineno, int *last_column);
 
-void rb_iseq_remove_coverage_all();
+void rb_iseq_remove_coverage_all(void);
 
 /* proc.c */
 const rb_iseq_t *rb_method_iseq(VALUE body);