diff --git a/iwyu_regex.cc b/iwyu_regex.cc
index eae94b3..2dc9e62 100644
--- a/iwyu_regex.cc
+++ b/iwyu_regex.cc
@@ -13,9 +13,31 @@
 #include "llvm/Support/Regex.h"
 
 #include "iwyu_port.h"
+#include "iwyu_string_util.h"
 
 namespace include_what_you_use {
 
+namespace {
+
+// Add ^...$ start/end anchoring if they don't already exist.
+// This is useful to transform from search-inside-string semantics to match-
+// whole-string semantics for regex implementations that don't support the
+// latter.
+std::string Anchored(const std::string& pattern) {
+  const char* prefix = "";
+  const char* suffix = "";
+  if (!StartsWith(pattern, "^")) {
+    prefix = "^";
+  }
+  if (!EndsWith(pattern, "$")) {
+    suffix = "$";
+  }
+
+  return prefix + pattern + suffix;
+}
+
+}  // anonymous namespace
+
 bool ParseRegexDialect(const char* str, RegexDialect* dialect) {
   if (strcmp(str, "llvm") == 0) {
     *dialect = RegexDialect::LLVM;
@@ -31,9 +53,8 @@ bool RegexMatch(RegexDialect dialect, const std::string& str,
                 const std::string& pattern) {
   switch (dialect) {
     case RegexDialect::LLVM: {
-      // llvm::Regex::match has search semantics. Enclose the pattern in ^...$
-      // for start/end anchoring.
-      llvm::Regex r("^" + pattern + "$");
+      // llvm::Regex::match has search semantics; ensure anchored.
+      llvm::Regex r(Anchored(pattern));
       return r.match(str);
     }
 
@@ -50,16 +71,14 @@ std::string RegexReplace(RegexDialect dialect, const std::string& str,
                          const std::string& replacement) {
   switch (dialect) {
     case RegexDialect::LLVM: {
-      // llvm::Regex::sub  has search semantics. Enclose the pattern in ^...$
-      // for start/end anchoring.
-      llvm::Regex r("^" + pattern + "$");
+      // llvm::Regex::sub has search semantics; ensure anchored.
+      llvm::Regex r(Anchored(pattern));
       return r.sub(replacement, str);
     }
 
     case RegexDialect::ECMAScript: {
-      // std::regex_replace has search semantics. Enclose the pattern in ^...$
-      // for start/end anchoring.
-      std::regex r("^" + pattern + "$", std::regex_constants::ECMAScript);
+      // std::regex_replace has search semantics; ensure anchored.
+      std::regex r(Anchored(pattern), std::regex_constants::ECMAScript);
       return std::regex_replace(str, r, replacement,
                                 std::regex_constants::format_first_only);
     }