diff --git a/src/tool_cb_hdr.c b/src/tool_cb_hdr.c
index 5de973470..6e23d1da8 100644
--- a/src/tool_cb_hdr.c
+++ b/src/tool_cb_hdr.c
@@ -40,7 +40,7 @@ static char *parse_filename(const char *ptr, size_t len);
 ** callback for CURLOPT_HEADERFUNCTION
 */
 
-size_t tool_header_cb(void *ptr, size_t size, size_t nmemb, void *userdata)
+size_t tool_header_cb(char *ptr, size_t size, size_t nmemb, void *userdata)
 {
   struct HdrCbData *hdrcbdata = userdata;
   struct OutStruct *outs = hdrcbdata->outs;
diff --git a/src/tool_cb_hdr.h b/src/tool_cb_hdr.h
index bb54bbb88..32032e980 100644
--- a/src/tool_cb_hdr.h
+++ b/src/tool_cb_hdr.h
@@ -48,7 +48,7 @@ struct HdrCbData {
 ** callback for CURLOPT_HEADERFUNCTION
 */
 
-size_t tool_header_cb(void *ptr, size_t size, size_t nmemb, void *userdata);
+size_t tool_header_cb(char *ptr, size_t size, size_t nmemb, void *userdata);
 
 #endif /* HEADER_CURL_TOOL_CB_HDR_H */
 
diff --git a/src/tool_cb_wrt.c b/src/tool_cb_wrt.c
index 041345762..5c28a2cf8 100644
--- a/src/tool_cb_wrt.c
+++ b/src/tool_cb_wrt.c
@@ -72,7 +72,7 @@ bool tool_create_output_file(struct OutStruct *outs)
 ** callback for CURLOPT_WRITEFUNCTION
 */
 
-size_t tool_write_cb(void *buffer, size_t sz, size_t nmemb, void *userdata)
+size_t tool_write_cb(char *buffer, size_t sz, size_t nmemb, void *userdata)
 {
   size_t rc;
   struct OutStruct *outs = userdata;
diff --git a/src/tool_cb_wrt.h b/src/tool_cb_wrt.h
index fc60be0fc..4ccbf3a5f 100644
--- a/src/tool_cb_wrt.h
+++ b/src/tool_cb_wrt.h
@@ -27,7 +27,7 @@
 ** callback for CURLOPT_WRITEFUNCTION
 */
 
-size_t tool_write_cb(void *buffer, size_t sz, size_t nmemb, void *userdata);
+size_t tool_write_cb(char *buffer, size_t sz, size_t nmemb, void *userdata);
 
 /* create a local file for writing, return TRUE on success */
 bool tool_create_output_file(struct OutStruct *outs);