diff --git a/xmlsave.c b/xmlsave.c
index 24b279c9..d0492ee4 100644
--- a/xmlsave.c
+++ b/xmlsave.c
@@ -128,7 +128,7 @@ static const char xmlEscapeContent[] = {
     ';',
 };
 
-static const char xmlEscapeTab[128] = {
+static const signed char xmlEscapeTab[128] = {
      0,  0,  0,  0,  0,  0,  0,  0,  0, -1, -1,  0,  0, 20,  0,  0,
      0,  0,  0,  0, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
     -1, -1, -1, -1, -1, -1, 33, -1, -1, -1, -1, -1, -1, -1, -1, -1,
@@ -139,7 +139,7 @@ static const char xmlEscapeTab[128] = {
     -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
 };
 
-static const char xmlEscapeTabAttr[128] = {
+static const signed char xmlEscapeTabAttr[128] = {
      0,  0,  0,  0,  0,  0,  0,  0,  0,  9, 14,  0,  0, 20,  0,  0,
      0,  0,  0,  0, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
     -1, -1, 26, -1, -1, -1, 33, -1, -1, -1, -1, -1, -1, -1, -1, -1,
@@ -154,7 +154,7 @@ static void
 xmlSerializeText(xmlOutputBufferPtr buf, const xmlChar *string,
                  unsigned flags) {
     const char *cur;
-    const char *tab;
+    const signed char *tab;
 
     if (string == NULL)
         return;