diff --git a/libbacktrace/Backtrace.cpp b/libbacktrace/Backtrace.cpp
index 9ead452..555e8cf 100644
--- a/libbacktrace/Backtrace.cpp
+++ b/libbacktrace/Backtrace.cpp
@@ -93,16 +93,26 @@
 }
 
 std::string Backtrace::FormatFrameData(const backtrace_frame_data_t* frame) {
-  const char* map_name;
-  if (BacktraceMap::IsValid(frame->map) && !frame->map.name.empty()) {
-    map_name = frame->map.name.c_str();
+  uintptr_t relative_pc;
+  std::string map_name;
+  if (BacktraceMap::IsValid(frame->map)) {
+    relative_pc = BacktraceMap::GetRelativePc(frame->map, frame->pc);
+    if (!frame->map.name.empty()) {
+      map_name = frame->map.name.c_str();
+      if (map_name[0] == '[' && map_name[map_name.size() - 1] == ']') {
+        map_name.resize(map_name.size() - 1);
+        map_name += StringPrintf(":%" PRIPTR "]", frame->map.start);
+      }
+    } else {
+      map_name = StringPrintf("<anonymous:%" PRIPTR ">", frame->map.start);
+    }
   } else {
     map_name = "<unknown>";
+    relative_pc = frame->pc;
   }
 
-  uintptr_t relative_pc = BacktraceMap::GetRelativePc(frame->map, frame->pc);
-
-  std::string line(StringPrintf("#%02zu pc %" PRIPTR "  %s", frame->num, relative_pc, map_name));
+  std::string line(StringPrintf("#%02zu pc %" PRIPTR "  ", frame->num, relative_pc));
+  line += map_name;
   // Special handling for non-zero offset maps, we need to print that
   // information.
   if (frame->map.offset != 0) {
diff --git a/libbacktrace/backtrace_test.cpp b/libbacktrace/backtrace_test.cpp
index 9ebd639..ce04817 100644
--- a/libbacktrace/backtrace_test.cpp
+++ b/libbacktrace/backtrace_test.cpp
@@ -775,16 +775,29 @@
             backtrace->FormatFrameData(&frame));
 
   // Check map name empty, but exists.
-  frame.map.start = 1;
-  frame.map.end = 1;
+  frame.pc = 0xb0020;
+  frame.map.start = 0xb0000;
+  frame.map.end = 0xbffff;
   frame.map.load_base = 0;
 #if defined(__LP64__)
-  EXPECT_EQ("#01 pc 0000000000000001  <unknown>",
+  EXPECT_EQ("#01 pc 0000000000000020  <anonymous:00000000000b0000>",
 #else
-  EXPECT_EQ("#01 pc 00000001  <unknown>",
+  EXPECT_EQ("#01 pc 00000020  <anonymous:000b0000>",
 #endif
             backtrace->FormatFrameData(&frame));
 
+  // Check map name begins with a [.
+  frame.pc = 0xc0020;
+  frame.map.start = 0xc0000;
+  frame.map.end = 0xcffff;
+  frame.map.load_base = 0;
+  frame.map.name = "[anon:thread signal stack]";
+#if defined(__LP64__)
+  EXPECT_EQ("#01 pc 0000000000000020  [anon:thread signal stack:00000000000c0000]",
+#else
+  EXPECT_EQ("#01 pc 00000020  [anon:thread signal stack:000c0000]",
+#endif
+            backtrace->FormatFrameData(&frame));
 
   // Check relative pc is set and map name is set.
   frame.pc = 0x12345679;