diff --git a/src/text/scrptrun.cpp b/src/text/scrptrun.cpp
index 750998764..bc16cb811 100644
--- a/src/text/scrptrun.cpp
+++ b/src/text/scrptrun.cpp
@@ -21,8 +21,13 @@
 #pragma GCC diagnostic pop
 
 #include <mapnik/text/scrptrun.hpp>
+#include <cstddef>
 
-#define ARRAY_SIZE(array) (sizeof(array) / sizeof(array[0]))
+template <class T, std::size_t N>
+constexpr std::size_t ARRAY_SIZE(const T (&array)[N]) noexcept
+{
+    return N;
+}
 
 const char ScriptRun::fgClassID=0;
 
@@ -156,7 +161,8 @@ UBool ScriptRun::next()
         // characters above it on the stack will be poped.
         if (pairIndex >= 0) {
             if ((pairIndex & 1) == 0) {
-                parenStack[++parenSP].pairIndex = pairIndex;
+                parenSP = (++parenSP) % ARRAY_SIZE(parenStack); // avoid out-of-bounds access
+                parenStack[parenSP].pairIndex = pairIndex;
                 parenStack[parenSP].scriptCode  = scriptCode;
             } else if (parenSP >= 0) {
                 int32_t pi = pairIndex & ~1;