diff --git a/stdlib/runtime/Debug.h b/stdlib/runtime/Debug.h
index f00dd246600..802d624f7dd 100644
--- a/stdlib/runtime/Debug.h
+++ b/stdlib/runtime/Debug.h
@@ -28,6 +28,9 @@
 
 namespace swift {
 
+// swift::crash() halts with a crash log message, 
+// but otherwise tries not to disturb register state.
+
 LLVM_ATTRIBUTE_NORETURN
 LLVM_ATTRIBUTE_ALWAYS_INLINE // Minimize trashed registers
 static void crash(const char *message) {
@@ -41,6 +44,12 @@ static void crash(const char *message) {
   __builtin_unreachable();
 }
 
+// swift::fatalError() halts with a crash log message, 
+// but makes no attempt to preserve register state.
+LLVM_ATTRIBUTE_NORETURN
+extern void
+fatalError(const char *format, ...);
+
 };
 
 #endif // _SWIFT_RUNTIME_DEBUG_HELPERS_
diff --git a/stdlib/runtime/Errors.cpp b/stdlib/runtime/Errors.cpp
index 33e223a1480..a4e239c6a37 100644
--- a/stdlib/runtime/Errors.cpp
+++ b/stdlib/runtime/Errors.cpp
@@ -22,6 +22,7 @@
 #include <pthread.h>
 #include <malloc/malloc.h>
 #include <asl.h>
+#include "Debug.h"
 
 
 #if SWIFT_HAVE_CRASHREPORTERCLIENT
@@ -70,6 +71,24 @@ reportNow(const char *message)
 }
 
 
+// Report a fatal error to system console, stderr, and crash logs, then abort.
+LLVM_ATTRIBUTE_NORETURN
+void
+swift::fatalError(const char *format, ...)
+{
+  va_list args;
+  va_start(args, format);
+
+  char *log;
+  vasprintf(&log, format, args);
+
+  reportNow(log);
+  reportOnCrash(log);
+
+  abort();
+}
+
+
 // Report a fatal error to system console, stderr, and crash logs.
 // <prefix>: <message>: file <file>, line <line>\n
 // The message may be omitted by passing messageLength=0.
diff --git a/stdlib/runtime/SwiftObject.mm b/stdlib/runtime/SwiftObject.mm
index a4c27e7a8d2..1af97ca2ee1 100644
--- a/stdlib/runtime/SwiftObject.mm
+++ b/stdlib/runtime/SwiftObject.mm
@@ -182,7 +182,10 @@ static NSString *_getDescription(SwiftObject *obj) {
 }
 
 - (void)doesNotRecognizeSelector: (SEL) sel {
-  swift::crash("Unrecognized selector");
+  Class cls = object_getClass(self);
+  fatalError("Unrecognized selector %c[%s %s]\n", 
+             class_isMetaClass(cls) ? '+' : '-', 
+             class_getName(cls), sel_getName(sel));
 }
 
 - (id)retain {