diff --git a/src/ctype.c b/src/ctype.c
index ad0e0976..1355a4ee 100644
--- a/src/ctype.c
+++ b/src/ctype.c
@@ -175,8 +175,22 @@ int ucd_isspace(codepoint_t c)
 
 int ucd_isupper(codepoint_t c)
 {
-	return ucd_lookup_category(c) == UCD_CATEGORY_Lu
-	    || ucd_tolower(c) != c;
+	switch (ucd_lookup_category(c))
+	{
+	case UCD_CATEGORY_Lu:
+		return 1;
+	case UCD_CATEGORY_Lt:
+		return ucd_tolower(c) != c;
+	case UCD_CATEGORY_Nl:
+		return (c >= 0x002160 && c <= 0x00216F); // Other_Uppercase
+	case UCD_CATEGORY_So:
+		return (c >= 0x0024B6 && c <= 0x0024CF)  // Other_Uppercase
+		    || (c >= 0x01F130 && c <= 0x01F149)  // Other_Uppercase
+		    || (c >= 0x01F150 && c <= 0x01F169)  // Other_Uppercase
+		    || (c >= 0x01F170 && c <= 0x01F189); // Other_Uppercase
+	default:
+		return 0;
+	}
 }
 
 int ucd_isxdigit(codepoint_t c)
diff --git a/tools/printdata.py b/tools/printdata.py
index 0bee85e2..6e84c67c 100755
--- a/tools/printdata.py
+++ b/tools/printdata.py
@@ -100,9 +100,11 @@ def isalpha(data):
 		return 0
 
 def isupper(data):
-	if data.get('LowerCase', null) != null:
+	if data.get('GeneralCategory', 'Cn') == 'Lu':
 		return 1
-	elif data.get('GeneralCategory', 'Cn') == 'Lu':
+	elif data.get('Other_Uppercase', 0):
+		return 1
+	elif data.get('LowerCase', null) != null: # Some Lt characters have lowercase forms.
 		return 1
 	else:
 		return 0