diff --git a/src/regexp/jsregexp.cc b/src/regexp/jsregexp.cc
index a26a1d77ce..30e39f7c5c 100644
--- a/src/regexp/jsregexp.cc
+++ b/src/regexp/jsregexp.cc
@@ -2768,16 +2768,13 @@ RegExpNode* TextNode::FilterOneByte(int depth) {
       Vector<const uc16> quarks = elm.atom()->data();
       for (int j = 0; j < quarks.length(); j++) {
         uint16_t c = quarks[j];
-        if (c <= String::kMaxOneByteCharCode) continue;
-        if (!IgnoreCase(elm.atom()->flags())) return set_replacement(nullptr);
-        // Here, we need to check for characters whose upper and lower cases
-        // are outside the Latin-1 range.
-        uint16_t converted = unibrow::Latin1::ConvertNonLatin1ToLatin1(c);
-        // Character is outside Latin-1 completely
-        if (converted == 0) return set_replacement(nullptr);
-        // Convert quark to Latin-1 in place.
-        uint16_t* copy = const_cast<uint16_t*>(quarks.start());
-        copy[j] = converted;
+        if (elm.atom()->ignore_case()) {
+          c = unibrow::Latin1::TryConvertToLatin1(c);
+        }
+        if (c > unibrow::Latin1::kMaxChar) return set_replacement(nullptr);
+        // Replace quark in case we converted to Latin-1.
+        uint16_t* writable_quarks = const_cast<uint16_t*>(quarks.start());
+        writable_quarks[j] = c;
       }
     } else {
       DCHECK(elm.text_type() == TextElement::CHAR_CLASS);
@@ -3209,10 +3206,17 @@ void TextNode::TextEmitPass(RegExpCompiler* compiler,
         if (first_element_checked && i == 0 && j == 0) continue;
         if (DeterminedAlready(quick_check, elm.cp_offset() + j)) continue;
         EmitCharacterFunction* emit_function = nullptr;
+        uc16 quark = quarks[j];
+        if (elm.atom()->ignore_case()) {
+          // Everywhere else we assume that a non-Latin-1 character cannot match
+          // a Latin-1 character. Avoid the cases where this is assumption is
+          // invalid by using the Latin1 equivalent instead.
+          quark = unibrow::Latin1::TryConvertToLatin1(quark);
+        }
         switch (pass) {
           case NON_LATIN1_MATCH:
             DCHECK(one_byte);
-            if (quarks[j] > String::kMaxOneByteCharCode) {
+            if (quark > String::kMaxOneByteCharCode) {
               assembler->GoTo(backtrack);
               return;
             }
@@ -3232,8 +3236,8 @@ void TextNode::TextEmitPass(RegExpCompiler* compiler,
         if (emit_function != nullptr) {
           bool bounds_check = *checked_up_to < cp_offset + j || read_backward();
           bool bound_checked =
-              emit_function(isolate, compiler, quarks[j], backtrack,
-                            cp_offset + j, bounds_check, preloaded);
+              emit_function(isolate, compiler, quark, backtrack, cp_offset + j,
+                            bounds_check, preloaded);
           if (bound_checked) UpdateBoundsCheck(cp_offset + j, checked_up_to);
         }
       }
diff --git a/src/unicode-decoder.h b/src/unicode-decoder.h
index 38a1837af3..97f551f4c6 100644
--- a/src/unicode-decoder.h
+++ b/src/unicode-decoder.h
@@ -93,15 +93,11 @@ size_t Utf8Decoder<kBufferSize>::WriteUtf16(uint16_t* data,
 class Latin1 {
  public:
   static const unsigned kMaxChar = 0xff;
-  // Returns 0 if character does not convert to single latin-1 character
-  // or if the character doesn't not convert back to latin-1 via inverse
-  // operation (upper to lower, etc).
-  static inline uint16_t ConvertNonLatin1ToLatin1(uint16_t);
+  // Convert the character to Latin-1 case equivalent if possible.
+  static inline uint16_t TryConvertToLatin1(uint16_t);
 };
 
-
-uint16_t Latin1::ConvertNonLatin1ToLatin1(uint16_t c) {
-  DCHECK_GT(c, Latin1::kMaxChar);
+uint16_t Latin1::TryConvertToLatin1(uint16_t c) {
   switch (c) {
     // This are equivalent characters in unicode.
     case 0x39c:
@@ -112,7 +108,7 @@ uint16_t Latin1::ConvertNonLatin1ToLatin1(uint16_t c) {
     case 0x178:
       return 0xff;
   }
-  return 0;
+  return c;
 }
 
 
diff --git a/test/cctest/test-strings.cc b/test/cctest/test-strings.cc
index ba6186828d..1cdcf77fa7 100644
--- a/test/cctest/test-strings.cc
+++ b/test/cctest/test-strings.cc
@@ -1505,7 +1505,7 @@ static uint16_t ConvertLatin1(uint16_t c) {
 #ifndef V8_INTL_SUPPORT
 static void CheckCanonicalEquivalence(uint16_t c, uint16_t test) {
   uint16_t expect = ConvertLatin1<unibrow::Ecma262UnCanonicalize, true>(c);
-  if (expect > unibrow::Latin1::kMaxChar) expect = 0;
+  if (expect > unibrow::Latin1::kMaxChar || expect == 0) expect = c;
   CHECK_EQ(expect, test);
 }
 
@@ -1514,7 +1514,7 @@ TEST(Latin1IgnoreCase) {
   for (uint16_t c = unibrow::Latin1::kMaxChar + 1; c != 0; c++) {
     uint16_t lower = ConvertLatin1<unibrow::ToLowercase, false>(c);
     uint16_t upper = ConvertLatin1<unibrow::ToUppercase, false>(c);
-    uint16_t test = unibrow::Latin1::ConvertNonLatin1ToLatin1(c);
+    uint16_t test = unibrow::Latin1::TryConvertToLatin1(c);
     // Filter out all character whose upper is not their lower or vice versa.
     if (lower == 0 && upper == 0) {
       CheckCanonicalEquivalence(c, test);
diff --git a/test/mjsunit/regress/regress-6703.js b/test/mjsunit/regress/regress-6703.js
new file mode 100644
index 0000000000..82bf21d55e
--- /dev/null
+++ b/test/mjsunit/regress/regress-6703.js
@@ -0,0 +1,23 @@
+// Copyright 2018 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+assertTrue(/(\u039C)/i.test("\xB5"));
+assertTrue(/(\u039C)+/i.test("\xB5"));
+assertTrue(/(\u039C)/ui.test("\xB5"));
+assertTrue(/(\u039C)+/ui.test("\xB5"));
+
+assertTrue(/(\u03BC)/i.test("\xB5"));
+assertTrue(/(\u03BC)+/i.test("\xB5"));
+assertTrue(/(\u03BC)/ui.test("\xB5"));
+assertTrue(/(\u03BC)+/ui.test("\xB5"));
+
+assertTrue(/(\u03BC)/i.test("\u039C"));
+assertTrue(/(\u03BC)+/i.test("\u039C"));
+assertTrue(/(\u03BC)/ui.test("\u039C"));
+assertTrue(/(\u03BC)+/ui.test("\u039C"));
+
+assertTrue(/(\u0178)/i.test("\xFF"));
+assertTrue(/(\u0178)+/i.test("\xFF"));
+assertTrue(/(\u0178)/ui.test("\xFF"));
+assertTrue(/(\u0178)+/ui.test("\xFF"));