diff --git a/liblog/event_tag_map.cpp b/liblog/event_tag_map.cpp
index 0b977c2..73ed16f 100644
--- a/liblog/event_tag_map.cpp
+++ b/liblog/event_tag_map.cpp
@@ -229,9 +229,16 @@
   return it->second;
 }
 
+// The position after the end of a valid section of the tag string,
+// caller makes sure delimited appropriately.
+static const char* endOfTag(const char* cp) {
+  while (*cp && (isalnum(*cp) || strchr("_.-@,", *cp))) ++cp;
+  return cp;
+}
+
 // Scan one tag line.
 //
-// "*pData" should be pointing to the first digit in the tag number.  On
+// "pData" should be pointing to the first digit in the tag number.  On
 // successful return, it will be pointing to the last character in the
 // tag line (i.e. the character before the start of the next line).
 //
@@ -241,10 +248,11 @@
 // data and it will outlive the call.
 //
 // Returns 0 on success, nonzero on failure.
-static int scanTagLine(EventTagMap* map, char** pData, int lineNum) {
-  char* cp;
-  unsigned long val = strtoul(*pData, &cp, 10);
-  if (cp == *pData) {
+static int scanTagLine(EventTagMap* map, const char*& pData, int lineNum) {
+  char* ep;
+  unsigned long val = strtoul(pData, &ep, 10);
+  const char* cp = ep;
+  if (cp == pData) {
     if (lineNum) {
       fprintf(stderr, OUT_TAG ": malformed tag number on line %d\n", lineNum);
     }
@@ -273,14 +281,13 @@
   }
 
   const char* tag = cp;
-  // Determine whether "c" is a valid tag char.
-  while (isalnum(*++cp) || (*cp == '_')) {
-  }
+  cp = endOfTag(cp);
   size_t tagLen = cp - tag;
 
   if (!isspace(*cp)) {
     if (lineNum) {
-      fprintf(stderr, OUT_TAG ": invalid tag chars on line %d\n", lineNum);
+      fprintf(stderr, OUT_TAG ": invalid tag char %c on line %d\n", *cp,
+              lineNum);
     }
     errno = EINVAL;
     return -1;
@@ -311,9 +318,9 @@
 
   while (*cp != '\n') ++cp;
 #ifdef DEBUG
-  fprintf(stderr, "%d: %p: %.*s\n", lineNum, tag, (int)(cp - *pData), *pData);
+  fprintf(stderr, "%d: %p: %.*s\n", lineNum, tag, (int)(cp - pData), pData);
 #endif
-  *pData = cp;
+  pData = cp;
 
   if (lineNum) {
     if (map->emplaceUnique(tagIndex,
@@ -341,9 +348,9 @@
 
 // Parse the tags out of the file.
 static int parseMapLines(EventTagMap* map, size_t which) {
-  char* cp = static_cast<char*>(map->mapAddr[which]);
+  const char* cp = static_cast<char*>(map->mapAddr[which]);
   size_t len = map->mapLen[which];
-  char* endp = cp + len;
+  const char* endp = cp + len;
 
   // insist on EOL at EOF; simplifies parsing and null-termination
   if (!len || (*(endp - 1) != '\n')) {
@@ -370,7 +377,7 @@
         lineStart = false;
       } else if (isdigit(*cp)) {
         // looks like a tag; scan it out
-        if (scanTagLine(map, &cp, lineNum) != 0) {
+        if (scanTagLine(map, cp, lineNum) != 0) {
           if (!which || (errno != EMLINK)) {
             return -1;
           }
@@ -495,14 +502,13 @@
   int ret = asprintf(&buf, command_template, tag);
   if (ret > 0) {
     // Add some buffer margin for an estimate of the full return content.
-    char* cp;
     size_t size =
         ret - strlen(command_template) +
         strlen("65535\n4294967295\t?\t\t\t?\t# uid=32767\n\n\f?success?");
     if (size > (size_t)ret) {
-      cp = static_cast<char*>(realloc(buf, size));
-      if (cp) {
-        buf = cp;
+      char* np = static_cast<char*>(realloc(buf, size));
+      if (np) {
+        buf = np;
       } else {
         size = ret;
       }
@@ -512,10 +518,12 @@
     // Ask event log tag service for an existing entry
     if (__send_log_msg(buf, size) >= 0) {
       buf[size - 1] = '\0';
-      unsigned long val = strtoul(buf, &cp, 10);        // return size
+      char* ep;
+      unsigned long val = strtoul(buf, &ep, 10);  // return size
+      const char* cp = ep;
       if ((buf != cp) && (val > 0) && (*cp == '\n')) {  // truncation OK
         ++cp;
-        if (!scanTagLine(map, &cp, 0)) {
+        if (!scanTagLine(map, cp, 0)) {
           free(buf);
           return map->find(tag);
         }
@@ -573,8 +581,9 @@
 LIBLOG_ABI_PUBLIC int android_lookupEventTagNum(EventTagMap* map,
                                                 const char* tagname,
                                                 const char* format, int prio) {
-  size_t len = strlen(tagname);
-  if (!len) {
+  const char* ep = endOfTag(tagname);
+  size_t len = ep - tagname;
+  if (!len || *ep) {
     errno = EINVAL;
     return -1;
   }
diff --git a/logcat/tests/logcat_test.cpp b/logcat/tests/logcat_test.cpp
index 33355e4..e487a97 100644
--- a/logcat/tests/logcat_test.cpp
+++ b/logcat/tests/logcat_test.cpp
@@ -1677,7 +1677,7 @@
         // Invent new entries because existing can not serve
         EventTagMap* map = android_openEventTagMap(nullptr);
         ASSERT_TRUE(nullptr != map);
-        static const char name[] = ___STRING(logcat) "_descriptive_monotonic";
+        static const char name[] = ___STRING(logcat) ".descriptive-monotonic";
         int myTag = android_lookupEventTagNum(map, name, "(new|1|s)",
                                               ANDROID_LOG_UNKNOWN);
         android_closeEventTagMap(map);