Index: llvm/trunk/lib/MC/ELFObjectWriter.cpp
===================================================================
--- llvm/trunk/lib/MC/ELFObjectWriter.cpp
+++ llvm/trunk/lib/MC/ELFObjectWriter.cpp
@@ -420,6 +420,10 @@
         !Rest.startswith("@@@"))
       report_fatal_error("A @@ version cannot be undefined");
 
+    if (Renames.count(&Symbol) && Renames[&Symbol] != Alias)
+      report_fatal_error(llvm::Twine("Multiple symbol versions defined for ") +
+                         Symbol.getName());
+
     Renames.insert(std::make_pair(&Symbol, Alias));
   }
 }
Index: llvm/trunk/test/MC/ELF/multiple-different-symver.s
===================================================================
--- llvm/trunk/test/MC/ELF/multiple-different-symver.s
+++ llvm/trunk/test/MC/ELF/multiple-different-symver.s
@@ -0,0 +1,6 @@
+// RUN: not llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o %t 2>&1 | FileCheck %s
+
+// CHECK: Multiple symbol versions defined for foo
+
+.symver foo, foo@1
+.symver foo, foo@2
Index: llvm/trunk/test/MC/ELF/multiple-equiv-symver.s
===================================================================
--- llvm/trunk/test/MC/ELF/multiple-equiv-symver.s
+++ llvm/trunk/test/MC/ELF/multiple-equiv-symver.s
@@ -0,0 +1,6 @@
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - 2>&1 | FileCheck %s
+
+// CHECK-NOT: Multiple symbol versions defined for foo
+
+.symver foo, foo@1
+.symver foo, foo@1