diff --git a/include/sigar_util.h b/include/sigar_util.h
index 0f56aeec..81b24bc8 100644
--- a/include/sigar_util.h
+++ b/include/sigar_util.h
@@ -41,6 +41,9 @@
 #define sigar_isalpha(c) \
     (isalpha(((unsigned char)(c))))
 
+#define sigar_isupper(c) \
+    (isupper(((unsigned char)(c))))
+
 #ifndef PROC_FS_ROOT
 #define PROC_FS_ROOT "/proc/"
 #endif
diff --git a/src/sigar_ptql.c b/src/sigar_ptql.c
index 774fe6e9..c3a080b5 100644
--- a/src/sigar_ptql.c
+++ b/src/sigar_ptql.c
@@ -899,7 +899,7 @@ static int ptql_branch_parse(char *query, ptql_parse_branch_t *branch)
     if (*query) {
         char flag;
 
-        while (isupper((flag = *query))) {
+        while (sigar_isupper((flag = *query))) {
             switch (flag) {
               case 'P':
                 branch->op_flags |= PTQL_OP_FLAG_PARENT;