diff --git a/test/LLVMC/MultiplePluginPriorities.td b/test/LLVMC/MultiplePluginPriorities.td
new file mode 100644
index 0000000..721b7cc
--- /dev/null
+++ b/test/LLVMC/MultiplePluginPriorities.td
@@ -0,0 +1,10 @@
+// Check that multiple plugin priorities are not allowed.
+// RUN: ignore tblgen -I %p/../../include --gen-llvmc %s |& grep "More than one 'PluginPriority' instance found"
+
+include "llvm/CompilerDriver/Common.td"
+
+def Graph : CompilationGraph<[]>;
+
+def Priority1 : PluginPriority<1>;
+
+def Priority2 : PluginPriority<2>;
diff --git a/utils/TableGen/LLVMCConfigurationEmitter.cpp b/utils/TableGen/LLVMCConfigurationEmitter.cpp
index 06afaf7..6dfd1b3 100644
--- a/utils/TableGen/LLVMCConfigurationEmitter.cpp
+++ b/utils/TableGen/LLVMCConfigurationEmitter.cpp
@@ -775,11 +775,17 @@
 /// CalculatePriority - Calculate the priority of this plugin.
 int CalculatePriority(RecordVector::const_iterator B,
                       RecordVector::const_iterator E) {
-  int total = 0;
-  for (; B!=E; ++B) {
-    total += static_cast<int>((*B)->getValueAsInt("priority"));
+  int priority = 0;
+
+  if (B != E) {
+    priority  = static_cast<int>((*B)->getValueAsInt("priority"));
+
+    if (++B != E)
+      throw std::string("More than one 'PluginPriority' instance found: "
+                        "most probably an error!");
   }
-  return total;
+
+  return priority;
 }
 
 /// NotInGraph - Helper function object for FilterNotInGraph.