diff --git a/string.go b/string.go
index 95b68f3d..97758b28 100644
--- a/string.go
+++ b/string.go
@@ -431,8 +431,14 @@ func splitWordBoundaries(s string) []byte {
 			}
 			if i+2 < len(s) {
 				if e := s[i+2]; isASCIIUpper(c) && isASCIIUpper(d) && isASCIILower(e) {
-					out = append(out, c, ' ', d, e)
-					i += 3
+					// The lowercase letter only marks where the acronym ends: it
+					// opens the next word, so leave it for the following iteration.
+					// Consuming it here skips the boundary check on the pair it
+					// forms with the byte after it, which kept "Pv6" glued together
+					// in "IPv6Address" while "Int8Value" split the same
+					// letter/digit boundary.
+					out = append(out, c, ' ', d)
+					i += 2
 					continue
 				}
 			}
diff --git a/string_test.go b/string_test.go
index 639db529..a4d0a53a 100644
--- a/string_test.go
+++ b/string_test.go
@@ -492,6 +492,18 @@ func TestAllCase(t *testing.T) {
 			KebabCase:  "first-last",
 			SnakeCase:  "first_last",
 		}},
+		{in: "IPv6Address", want: output{
+			PascalCase: "IPv6Address",
+			CamelCase:  "iPv6Address",
+			KebabCase:  "i-pv-6-address",
+			SnakeCase:  "i_pv_6_address",
+		}},
+		{in: "HTMLv5Doc", want: output{
+			PascalCase: "HtmLv5Doc",
+			CamelCase:  "htmLv5Doc",
+			KebabCase:  "htm-lv-5-doc",
+			SnakeCase:  "htm_lv_5_doc",
+		}},
 	}
 
 	for _, tc := range testCases {
@@ -522,6 +534,9 @@ func TestWords(t *testing.T) {
 		{"UPPERCASE", []string{"UPPERCASE"}},
 		{"HTTPCode", []string{"HTTP", "Code"}},
 		{"Int8Value", []string{"Int", "8", "Value"}},
+		{"IPv6Address", []string{"I", "Pv", "6", "Address"}},
+		{"ABc1", []string{"A", "Bc", "1"}},
+		{"ABCdEf", []string{"AB", "Cd", "Ef"}},
 	}
 	for _, tc := range testCases {
 		tc := tc