Index: lldb/packages/Python/lldbsuite/test/python_api/thread/TestThreadAPI.py
===================================================================
--- lldb/packages/Python/lldbsuite/test/python_api/thread/TestThreadAPI.py
+++ lldb/packages/Python/lldbsuite/test/python_api/thread/TestThreadAPI.py
@@ -122,14 +122,20 @@
         self.assertTrue(
             thread.IsValid(),
             "There should be a thread stopped due to breakpoint")
-        #self.runCmd("process status")
-
-        # Due to the typemap magic (see lldb.swig), we pass in an (int)length to GetStopDescription
-        # and expect to get a Python string as the return object!
-        # The 100 is just an arbitrary number specifying the buffer size.
-        stop_description = thread.GetStopDescription(100)
-        self.expect(stop_description, exe=False,
-                    startstr='breakpoint')
+
+        # Get the stop reason. GetStopDescription expects that we pass in the size of the description
+        # we expect plus an additional byte for the null terminator.
+
+        # Test with a buffer that is exactly as large as the expected stop reason.
+        self.assertEqual("breakpoint 1.1", thread.GetStopDescription(len('breakpoint 1.1') + 1)
+
+        # Test some smaller buffer sizes.
+        self.assertEqual("breakpoint", thread.GetStopDescription(len('breakpoint') + 1))
+        self.assertEqual("break", thread.GetStopDescription(len('break') + 1)
+        self.assertEqual("b", thread.GetStopDescription(len('b') + 1)
+
+        # Test that we can pass in a much larger size and still get the right output.
+        self.assertEqual("breakpoint 1.1", thread.GetStopDescription(len('breakpoint 1.1') + 100)
 
     def step_out_of_malloc_into_function_b(self, exe_name):
         """Test Python SBThread.StepOut() API to step out of a malloc call where the call site is at function b()."""
Index: lldb/source/API/SBThread.cpp
===================================================================
--- lldb/source/API/SBThread.cpp
+++ lldb/source/API/SBThread.cpp
@@ -327,8 +327,13 @@
       if (stop_info_sp) {
         const char *stop_desc = stop_info_sp->GetDescription();
         if (stop_desc) {
-          if (dst)
-            return ::snprintf(dst, dst_len, "%s", stop_desc);
+          if (dst) {
+            ::snprintf(dst, dst_len, "%s", stop_desc);
+            // The string we return is either as long as buffer length minus null
+            // terminator or the number of characters in the description (depending
+            // which of these two is shorter).
+            return std::min(dst_len - 1, strlen(stop_desc));
+          }
           else {
             // NULL dst passed in, return the length needed to contain the
             // description