diff --git a/src/librssguard/3rd-party/mimesis/mimesis.cpp b/src/librssguard/3rd-party/mimesis/mimesis.cpp
index 7f812c0f0..81eb52813 100755
--- a/src/librssguard/3rd-party/mimesis/mimesis.cpp
+++ b/src/librssguard/3rd-party/mimesis/mimesis.cpp
@@ -38,7 +38,7 @@ using namespace std;
 
 namespace Mimesis {
   static const string base64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
-  static const char base64_inverse[256] = {
+  static const signed char base64_inverse[256] = {
     -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
     -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
     -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,