Index: compiler-rt/lib/sanitizer_common/sanitizer_flag_parser.h
===================================================================
--- compiler-rt/lib/sanitizer_common/sanitizer_flag_parser.h
+++ compiler-rt/lib/sanitizer_common/sanitizer_flag_parser.h
@@ -121,7 +121,7 @@
 
  private:
   void fatal_error(const char *err);
-  bool is_space(char c);
+  bool is_space();
   void skip_whitespace();
   void parse_flags();
   void parse_flag();
Index: compiler-rt/lib/sanitizer_common/sanitizer_flag_parser.cc
===================================================================
--- compiler-rt/lib/sanitizer_common/sanitizer_flag_parser.cc
+++ compiler-rt/lib/sanitizer_common/sanitizer_flag_parser.cc
@@ -67,18 +67,27 @@
   Die();
 }
 
-bool FlagParser::is_space(char c) {
-  return c == ' ' || c == ',' || c == ':' || c == '\n' || c == '\t' ||
-         c == '\r';
+bool FlagParser::is_space() {
+  char c = buf_[pos_];
+  if (c == ' ' || c == ',' || c == '\n' || c == '\t' || c == '\r')
+    return true;
+
+  // Treat ':' as an option separator unless it is immediately followed by a
+  // path separator. This avoids common portability issues when an unquoted
+  // Windows path is used, as in 'symbolizer_path=C:/foo/llvm-symbolizer.exe'.
+  // Since no option names should start with / or \, it should be unambiguous.
+  if (c == ':')
+    return buf_[pos_ + 1] != '\\' && buf_[pos_ + 1] != '/';
+  return false;
 }
 
 void FlagParser::skip_whitespace() {
-  while (is_space(buf_[pos_])) ++pos_;
+  while (is_space()) ++pos_;
 }
 
 void FlagParser::parse_flag() {
   uptr name_start = pos_;
-  while (buf_[pos_] != 0 && buf_[pos_] != '=' && !is_space(buf_[pos_])) ++pos_;
+  while (buf_[pos_] != 0 && buf_[pos_] != '=' && !is_space()) ++pos_;
   if (buf_[pos_] != '=') fatal_error("expected '='");
   char *name = ll_strndup(buf_ + name_start, pos_ - name_start);
 
@@ -91,8 +100,8 @@
     value = ll_strndup(buf_ + value_start + 1, pos_ - value_start - 1);
     ++pos_; // consume the closing quote
   } else {
-    while (buf_[pos_] != 0 && !is_space(buf_[pos_])) ++pos_;
-    if (buf_[pos_] != 0 && !is_space(buf_[pos_]))
+    while (buf_[pos_] != 0 && !is_space()) ++pos_;
+    if (buf_[pos_] != 0 && !is_space())
       fatal_error("expected separator or eol");
     value = ll_strndup(buf_ + value_start, pos_ - value_start);
   }
Index: compiler-rt/lib/sanitizer_common/tests/sanitizer_flags_test.cc
===================================================================
--- compiler-rt/lib/sanitizer_common/tests/sanitizer_flags_test.cc
+++ compiler-rt/lib/sanitizer_common/tests/sanitizer_flags_test.cc
@@ -177,4 +177,17 @@
   EXPECT_STREQ("path/two", cf.log_path);
 }
 
+TEST(SanitizerCommon, WindowsPath) {
+  FlagParser parser;
+  const char *p1 = "";
+  const char *p2 = "";
+  RegisterFlag(&parser, "path1", kFlagDesc, &p1);
+  RegisterFlag(&parser, "path2", kFlagDesc, &p2);
+  parser.ParseString("path1=C:/win/path.exe:path2=C:\\win\\path.exe");
+  ReportUnrecognizedFlags();
+
+  EXPECT_STREQ(p1, "C:/win/path.exe");
+  EXPECT_STREQ(p2, "C:\\win\\path.exe");
+}
+
 }  // namespace __sanitizer