diff --git a/fxjs/fx_date_helpers.cpp b/fxjs/fx_date_helpers.cpp
index 9feda50..15f762d 100644
--- a/fxjs/fx_date_helpers.cpp
+++ b/fxjs/fx_date_helpers.cpp
@@ -164,16 +164,11 @@
   }
 }
 
-// TODO(thestig): Consider returning a WideStringView to make this even faster.
-WideString ParseStringString(const WideString& str,
-                             size_t nStart,
-                             size_t* pSkip) {
+size_t FindSubWordLength(const WideString& str, size_t nStart) {
   size_t i = nStart;
   while (i < str.GetLength() && std::iswalnum(str[i]))
     ++i;
-
-  *pSkip = i - nStart;
-  return str.Mid(nStart, *pSkip);
+  return i - nStart;
 }
 
 }  // namespace
@@ -187,6 +182,9 @@
                                         L"July",    L"August",   L"September",
                                         L"October", L"November", L"December"};
 
+static constexpr size_t KMonthAbbreviationLength = 3;  // Anything in |kMonths|.
+static constexpr size_t kLongestFullMonthLength = 9;   // September
+
 double FX_GetDateTime() {
   if (!FSDK_IsSandBoxPolicyEnabled(FPDF_POLICY_MACHINETIME_ACCESS))
     return 0;
@@ -438,15 +436,18 @@
         } else if (remaining == 2 || format[i + 3] != c) {
           switch (c) {
             case 'm': {
-              WideString sMonth = ParseStringString(value, j, &nSkip);
               bool bFind = false;
-              for (size_t m = 0; m < FX_ArraySize(kMonths); ++m) {
-                if (sMonth.CompareNoCase(kMonths[m]) == 0) {
-                  nMonth = m + 1;
-                  i += 3;
-                  j += nSkip;
-                  bFind = true;
-                  break;
+              nSkip = FindSubWordLength(value, j);
+              if (nSkip == KMonthAbbreviationLength) {
+                WideString sMonth = value.Mid(j, KMonthAbbreviationLength);
+                for (size_t m = 0; m < FX_ArraySize(kMonths); ++m) {
+                  if (sMonth.CompareNoCase(kMonths[m]) == 0) {
+                    nMonth = m + 1;
+                    i += 3;
+                    j += nSkip;
+                    bFind = true;
+                    break;
+                  }
                 }
               }
 
@@ -472,18 +473,20 @@
               break;
             case 'm': {
               bool bFind = false;
-
-              WideString sMonth = ParseStringString(value, j, &nSkip);
-              sMonth.MakeLower();
-              for (size_t m = 0; m < FX_ArraySize(kFullMonths); ++m) {
-                WideString sFullMonths = WideString(kFullMonths[m]);
-                sFullMonths.MakeLower();
-                if (sFullMonths.Contains(sMonth.c_str())) {
-                  nMonth = m + 1;
-                  i += 4;
-                  j += nSkip;
-                  bFind = true;
-                  break;
+              nSkip = FindSubWordLength(value, j);
+              if (nSkip <= kLongestFullMonthLength) {
+                WideString sMonth = value.Mid(j, nSkip);
+                sMonth.MakeLower();
+                for (size_t m = 0; m < FX_ArraySize(kFullMonths); ++m) {
+                  WideString sFullMonths = WideString(kFullMonths[m]);
+                  sFullMonths.MakeLower();
+                  if (sFullMonths.Contains(sMonth.c_str())) {
+                    nMonth = m + 1;
+                    i += 4;
+                    j += nSkip;
+                    bFind = true;
+                    break;
+                  }
                 }
               }