diff --git a/src/runtime/c/gu/seq.c b/src/runtime/c/gu/seq.c
index 2c3d6c3e3..48a56fc24 100644
--- a/src/runtime/c/gu/seq.c
+++ b/src/runtime/c/gu/seq.c
@@ -272,7 +272,7 @@ gu_buf_sort(GuBuf *buf, GuOrder *order)
 }
 
 void*
-gu_seq_binsearch_(GuSeq *seq, GuOrder *order, size_t elem_size, void *key)
+gu_seq_binsearch_(GuSeq *seq, GuOrder *order, size_t elem_size, const void *key)
 {
 	int i = 0;
 	int j = seq->len-1;
@@ -296,7 +296,7 @@ gu_seq_binsearch_(GuSeq *seq, GuOrder *order, size_t elem_size, void *key)
 
 bool
 gu_seq_binsearch_index_(GuSeq *seq, GuOrder *order, size_t elem_size,
-                        void *key, size_t *pindex)
+                        const void *key, size_t *pindex)
 {
 	size_t i = 0;
 	size_t j = seq->len-1;
diff --git a/src/runtime/c/gu/seq.h b/src/runtime/c/gu/seq.h
index 5accb0b24..3143906f2 100644
--- a/src/runtime/c/gu/seq.h
+++ b/src/runtime/c/gu/seq.h
@@ -118,14 +118,14 @@ gu_buf_sort(GuBuf *buf, GuOrder *order);
 	((T*) gu_seq_binsearch_(S, O, sizeof(T), V))
 
 void*
-gu_seq_binsearch_(GuSeq *seq, GuOrder *order, size_t elem_size, void *key);
+gu_seq_binsearch_(GuSeq *seq, GuOrder *order, size_t elem_size, const void *key);
 
 #define gu_seq_binsearch_index(S, O, T, V, PI) \
 	gu_seq_binsearch_index_(S, O, sizeof(T), V, PI)
 
 bool
 gu_seq_binsearch_index_(GuSeq *seq, GuOrder *order, size_t elem_size, 
-                        void *key, size_t *pindex);
+                        const void *key, size_t *pindex);
 
 // Using a buffer as a heap
 void