diff --git a/osscan.cc b/osscan.cc
index d7ac3f863..f6bc3bbb6 100644
--- a/osscan.cc
+++ b/osscan.cc
@@ -992,7 +992,7 @@ void free_fingerprint_file(FingerPrintDB *DB) {
 }
 
 
-FingerPrintDB *parse_fingerprint_file(char *fname) {
+FingerPrintDB *parse_fingerprint_file(const char *fname) {
 FingerPrintDB *DB = NULL;
 FingerPrint *current;
 FILE *fp;
diff --git a/osscan.h b/osscan.h
index 3ef968ba6..ac84fcb63 100644
--- a/osscan.h
+++ b/osscan.h
@@ -130,7 +130,7 @@ FingerPrint *parse_single_fingerprint(char *fprint_orig);
 /* These functions take a file/db name and open+parse it, returning an
    (allocated) FingerPrintDB containing the results.  They exit with
    an error message in the case of error. */
-FingerPrintDB *parse_fingerprint_file(char *fname);
+FingerPrintDB *parse_fingerprint_file(const char *fname);
 FingerPrintDB *parse_fingerprint_reference_file(const char *dbname);
 
 void free_fingerprint_file(FingerPrintDB *DB);