diff --git a/src/common/unicode.cpp b/src/common/unicode.cpp
index 8d2a36a9..889cde0e 100644
--- a/src/common/unicode.cpp
+++ b/src/common/unicode.cpp
@@ -78,3 +78,12 @@ bool unicodeLatinAlpha (unsigned int c)
 }
 
 ////////////////////////////////////////////////////////////////////////////////
+// Digits 0-9.
+//
+// TODO This list should be derived from the Unicode database.
+bool unicodeLatinDigit (unsigned int c)
+{
+  return c >= 0x30 && c <= 0x39;
+}
+
+////////////////////////////////////////////////////////////////////////////////
diff --git a/src/common/unicode.h b/src/common/unicode.h
index 51c3b21c..bf4b3ff8 100644
--- a/src/common/unicode.h
+++ b/src/common/unicode.h
@@ -29,6 +29,7 @@
 
 bool unicodeWhitespace (unsigned int);
 bool unicodeLatinAlpha (unsigned int);
+bool unicodeLatinDigit (unsigned int);
 
 #endif
 ////////////////////////////////////////////////////////////////////////////////