diff --git a/lib/Bitcode/Reader/BitcodeReader.cpp b/lib/Bitcode/Reader/BitcodeReader.cpp
index ab0a1249f2d..f712d9db641 100644
--- a/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -960,7 +960,7 @@ error_code BitcodeReader::ParseValueSymbolTable() {
       if (ConvertToString(Record, 1, ValueName))
         return Error(InvalidRecord);
       unsigned ValueID = Record[0];
-      if (ValueID >= ValueList.size())
+      if (ValueID >= ValueList.size() || !ValueList[ValueID])
         return Error(InvalidRecord);
       Value *V = ValueList[ValueID];
 
@@ -1027,7 +1027,7 @@ error_code BitcodeReader::ParseMetadata() {
       unsigned Size = Record.size();
       NamedMDNode *NMD = TheModule->getOrInsertNamedMetadata(Name);
       for (unsigned i = 0; i != Size; ++i) {
-        MDNode *MD = dyn_cast<MDNode>(MDValueList.getValueFwdRef(Record[i]));
+        MDNode *MD = dyn_cast_or_null<MDNode>(MDValueList.getValueFwdRef(Record[i]));
         if (MD == 0)
           return Error(InvalidRecord);
         NMD->addOperand(MD);
@@ -1109,7 +1109,7 @@ error_code BitcodeReader::ResolveGlobalAndAliasInits() {
       // Not ready to resolve this yet, it requires something later in the file.
       GlobalInits.push_back(GlobalInitWorklist.back());
     } else {
-      if (Constant *C = dyn_cast<Constant>(ValueList[ValID]))
+      if (Constant *C = dyn_cast_or_null<Constant>(ValueList[ValID]))
         GlobalInitWorklist.back().first->setInitializer(C);
       else
         return Error(ExpectedConstant);
@@ -1122,7 +1122,7 @@ error_code BitcodeReader::ResolveGlobalAndAliasInits() {
     if (ValID >= ValueList.size()) {
       AliasInits.push_back(AliasInitWorklist.back());
     } else {
-      if (Constant *C = dyn_cast<Constant>(ValueList[ValID]))
+      if (Constant *C = dyn_cast_or_null<Constant>(ValueList[ValID]))
         AliasInitWorklist.back().first->setAliasee(C);
       else
         return Error(ExpectedConstant);
@@ -1135,7 +1135,7 @@ error_code BitcodeReader::ResolveGlobalAndAliasInits() {
     if (ValID >= ValueList.size()) {
       FunctionPrefixes.push_back(FunctionPrefixWorklist.back());
     } else {
-      if (Constant *C = dyn_cast<Constant>(ValueList[ValID]))
+      if (Constant *C = dyn_cast_or_null<Constant>(ValueList[ValID]))
         FunctionPrefixWorklist.back().first->setPrefixData(C);
       else
         return Error(ExpectedConstant);
@@ -1195,7 +1195,7 @@ error_code BitcodeReader::ParseConstants() {
     case bitc::CST_CODE_SETTYPE:   // SETTYPE: [typeid]
       if (Record.empty())
         return Error(InvalidRecord);
-      if (Record[0] >= TypeList.size())
+      if (Record[0] >= TypeList.size() || !TypeList[Record[0]])
         return Error(InvalidRecord);
       CurTy = TypeList[Record[0]];
       continue;  // Skip the ValueList manipulation.
@@ -3039,7 +3039,7 @@ OutOfRecordLoop:
     if (A->getParent() == 0) {
       // We found at least one unresolved value.  Nuke them all to avoid leaks.
       for (unsigned i = ModuleValueListSize, e = ValueList.size(); i != e; ++i){
-        if ((A = dyn_cast<Argument>(ValueList[i])) && A->getParent() == 0) {
+        if ((A = dyn_cast_or_null<Argument>(ValueList[i])) && A->getParent() == 0) {
           A->replaceAllUsesWith(UndefValue::get(A->getType()));
           delete A;
         }
diff --git a/test/Bitcode/pr18704.ll b/test/Bitcode/pr18704.ll
new file mode 100644
index 00000000000..f05fe53259f
--- /dev/null
+++ b/test/Bitcode/pr18704.ll
@@ -0,0 +1,158 @@
+; RUN:  not llvm-dis < %s.bc 2>&1 | FileCheck %s
+
+; CHECK: llvm-dis{{(\.EXE|\.exe)?}}: Never resolved value found in function
+
+; pr18704.ll.bc has an instruction referring to invalid type.
+; The test checks that LLVM reports the error and doesn't access freed memory
+; in doing so.
+
+;<MODULE_BLOCK NumWords=217 BlockCodeSize=3>
+;  <VERSION op0=1/>
+;  <BLOCKINFO_BLOCK/>
+;  <TYPE_BLOCK_ID NumWords=23 BlockCodeSize=4>
+;    <NUMENTRY op0=25/>
+;    <INTEGER op0=8/>
+;    <POINTER abbrevid=4 op0=0 op1=0/>
+;    <POINTER abbrevid=4 op0=1 op1=0/>
+;    <ARRAY abbrevid=9 op0=6 op1=0/>
+;    <POINTER abbrevid=4 op0=3 op1=0/>
+;    <ARRAY abbrevid=9 op0=10 op1=0/>
+;    <POINTER abbrevid=4 op0=5 op1=0/>
+;    <ARRAY abbrevid=9 op0=4 op1=0/>
+;    <POINTER abbrevid=4 op0=7 op1=0/>
+;    <ARRAY abbrevid=9 op0=5 op1=0/>
+;    <POINTER abbrevid=4 op0=9 op1=0/>
+;    <STRUCT_NAME abbrevid=7 op0=115 op1=116 op2=114 op3=117 op4=99 op5=116 op6=46 op7=112 op8=97 op9=105 op10=114 op11=46 op12=48/>
+;    <STRUCT_NAMED abbrevid=8 op0=0 op1=1 op2=1/>
+;    <ARRAY abbrevid=9 op0=2 op1=11/>
+;    <POINTER abbrevid=4 op0=12 op1=0/>
+;    <FUNCTION abbrevid=5 op0=0 op1=1 op2=1 op3=1/>
+;    <POINTER abbrevid=4 op0=14 op1=0/>
+;    <FUNCTION abbrevid=5 op0=0 op1=1 op2=1/>
+;    <POINTER abbrevid=4 op0=16 op1=0/>
+;    <INTEGER op0=64/>
+;    <FUNCTION abbrevid=5 op0=0 op1=1 op2=18/>
+;    <POINTER abbrevid=4 op0=19 op1=0/>
+;    <INTEGER op0=32/>
+;    <FUNCTION abbrevid=5 op0=0 op1=21/>
+;    <POINTER abbrevid=4 op0=22 op1=0/>
+;    <VOID/>
+;  </TYPE_BLOCK_ID>
+;  <GLOBALVAR abbrevid=4 op0=2 op1=0 op2=0 op3=0 op4=0 op5=0/>
+;  <GLOBALVAR abbrevid=4 op0=2 op1=0 op2=0 op3=0 op4=0 op5=0/>
+;  <GLOBALVAR abbrevid=4 op0=2 op1=0 op2=0 op3=0 op4=0 op5=0/>
+;  <GLOBALVAR op0=4 op1=1 op2=25 op3=9 op4=0 op5=0 op6=0 op7=0 op8=1 op9=0/>
+;  <GLOBALVAR op0=6 op1=1 op2=26 op3=9 op4=0 op5=0 op6=0 op7=0 op8=1 op9=0/>
+;  <GLOBALVAR op0=8 op1=1 op2=27 op3=9 op4=0 op5=0 op6=0 op7=0 op8=1 op9=0/>
+;  <GLOBALVAR abbrevid=4 op0=10 op1=1 op2=28 op3=3 op4=0 op5=0/>
+;  <GLOBALVAR abbrevid=4 op0=6 op1=1 op2=26 op3=3 op4=0 op5=0/>
+;  <GLOBALVAR abbrevid=4 op0=13 op1=1 op2=31 op3=3 op4=0 op5=0/>
+;  <GLOBALVAR abbrevid=4 op0=2 op1=1 op2=23 op3=3 op4=0 op5=0/>
+;  <GLOBALVAR abbrevid=4 op0=2 op1=0 op2=24 op3=0 op4=0 op5=0/>
+;  <GLOBALVAR op0=10 op1=1 op2=28 op3=9 op4=0 op5=0 op6=0 op7=0 op8=1 op9=0/>
+;  <FUNCTION op0=15 op1=0 op2=1 op3=0 op4=0 op5=0 op6=0 op7=0 op8=0 op9=0/>
+;  <FUNCTION op0=17 op1=0 op2=1 op3=0 op4=0 op5=0 op6=0 op7=0 op8=0 op9=0/>
+;  <FUNCTION op0=20 op1=0 op2=1 op3=0 op4=0 op5=0 op6=0 op7=0 op8=0 op9=0/>
+;  <FUNCTION op0=15 op1=0 op2=0 op3=0 op4=0 op5=0 op6=0 op7=0 op8=0 op9=0/>
+;  <FUNCTION op0=17 op1=0 op2=0 op3=0 op4=0 op5=0 op6=0 op7=0 op8=0 op9=0/>
+;  <FUNCTION op0=23 op1=0 op2=0 op3=0 op4=0 op5=0 op6=0 op7=0 op8=0 op9=0/>
+;  <CONSTANTS_BLOCK NumWords=20 BlockCodeSize=4>
+;    <SETTYPE abbrevid=4 op0=21/>
+;    <NULL/>
+;    <SETTYPE abbrevid=4 op0=1/>
+;    <CE_CAST abbrevid=6 op0=11 op1=17 op2=16/>
+;    <CE_INBOUNDS_GEP op0=6 op1=7 op2=21 op3=18 op4=21 op5=18/>
+;    <CE_CAST abbrevid=6 op0=11 op1=15 op2=15/>
+;    <CE_CAST abbrevid=6 op0=11 op1=13 op2=8/>
+;    <CE_CAST abbrevid=6 op0=11 op1=2 op2=9/>
+;    <SETTYPE abbrevid=4 op0=3/>
+;    <CSTRING abbrevid=11 op0=112 op1=114 op2=105 op3=110 op4=116/>
+;    <SETTYPE abbrevid=4 op0=5/>
+;    <CSTRING abbrevid=11 op0=115 op1=97 op2=121 op3=72 op4=105 op5=87 op6=105 op7=116 op8=104/>
+;    <SETTYPE abbrevid=4 op0=7/>
+;    <CSTRING abbrevid=11 op0=110 op1=101 op2=119/>
+;    <SETTYPE abbrevid=4 op0=9/>
+;    <CSTRING abbrevid=11 op0=109 op1=97 op2=105 op3=110/>
+;    <SETTYPE abbrevid=4 op0=11/>
+;    <AGGREGATE abbrevid=8 op0=31 op1=19/>
+;    <AGGREGATE abbrevid=8 op0=20 op1=21/>
+;    <SETTYPE abbrevid=4 op0=12/>
+;    <AGGREGATE abbrevid=8 op0=28 op1=29/>
+;    <SETTYPE abbrevid=4 op0=1/>
+;    <CE_INBOUNDS_GEP op0=10 op1=6 op2=21 op3=18 op4=21 op5=18/>
+;  </CONSTANTS_BLOCK>
+;  <METADATA_BLOCK NumWords=23 BlockCodeSize=3>
+;    <METADATA_KIND op0=0 op1=100 op2=98 op3=103/>
+;    <METADATA_KIND op0=1 op1=116 op2=98 op3=97 op4=97/>
+;    <METADATA_KIND op0=2 op1=112 op2=114 op3=111 op4=102/>
+;    <METADATA_KIND op0=3 op1=102 op2=112 op3=109 op4=97 op5=116 op6=104/>
+;    <METADATA_KIND op0=4 op1=114 op2=97 op3=110 op4=103 op5=101/>
+;    <METADATA_KIND op0=5 op1=116 op2=98 op3=97 op4=97 op5=46 op6=115 op7=116 op8=114 op9=117 op10=99 op11=116/>
+;    <METADATA_KIND op0=6 op1=105 op2=110 op3=118 op4=97 op5=114 op6=105 op7=97 op8=110 op9=116 op10=46 op11=108 op12=111 op13=97 op14=100/>
+;  </METADATA_BLOCK>
+;  <VALUE_SYMTAB NumWords=29 BlockCodeSize=4>
+;    <ENTRY abbrevid=6 op0=16 op1=101 op2=120 op3=97 op4=109 op5=112 op6=108 op7=101 op8=95 op9=109 op10=97 op11=105 op12=110/>
+;    <ENTRY abbrevid=6 op0=1 op1=99 op2=111 op3=110 op4=115 op5=111 op6=108 op7=101/>
+;    <ENTRY abbrevid=6 op0=2 op1=103 op2=114 op3=101 op4=101 op5=116 op6=105 op7=110 op8=103/>
+;    <ENTRY abbrevid=6 op0=15 op1=101 op2=120 op3=97 op4=109 op5=112 op6=108 op7=101 op8=95 op9=115 op10=97 op11=121 op12=72 op13=105 op14=87 op15=105 op16=116 op17=104/>
+;    <ENTRY abbrevid=6 op0=0 op1=115 op2=116 op3=114 op4=105 op5=110 op6=103/>
+;    <ENTRY abbrevid=6 op0=14 op1=109 op2=97 op3=108 op4=108 op5=111 op6=99/>
+;    <ENTRY abbrevid=6 op0=8 op1=101 op2=120 op3=97 op4=109 op5=112 op6=108 op7=101 op8=95 op9=118 op10=116 op11=97 op12=98/>
+;    <ENTRY abbrevid=6 op0=13 op1=115 op2=116 op3=114 op4=105 op5=110 op6=103 op7=95 op8=115 op9=116 op10=114 op11=105 op12=110 op13=103 op14=76 op15=105 op16=116 op17=101 op18=114 op19=97 op20=108/>
+;    <ENTRY abbrevid=6 op0=9 op1=95 op2=95 op3=101 op4=120 op5=97 op6=109 op7=112 op8=108 op9=101/>
+;    <ENTRY abbrevid=6 op0=12 op1=103 op2=101 op3=116 op4=102 op5=117 op6=110 op7=99/>
+;    <ENTRY abbrevid=6 op0=10 op1=101 op2=120 op3=97 op4=109 op5=112 op6=108 op7=101/>
+;    <ENTRY abbrevid=6 op0=17 op1=109 op2=97 op3=105 op4=110/>
+;  </VALUE_SYMTAB>
+;  <FUNCTION_BLOCK NumWords=18 BlockCodeSize=4>
+;    <DECLAREBLOCKS op0=1/>
+;    <CONSTANTS_BLOCK NumWords=3 BlockCodeSize=4>
+;      <SETTYPE abbrevid=4 op0=1/>
+;      <CE_INBOUNDS_GEP op0=4 op1=3 op2=21 op3=18 op4=21 op5=18/>
+;    </CONSTANTS_BLOCK>
+;    <INST_LOAD abbrevid=4 op0=34 op1=0 op2=0/>
+;    <INST_CALL op0=0 op1=0 op2=24 op3=1 op4=2/>
+;    <INST_CAST abbrevid=7 op0=1 op1=15 op2=11/>
+;    <INST_CALL op0=0 op1=0 op2=1 op3=3 op4=5/>
+;    <INST_RET abbrevid=9 op0=1/>
+;    <VALUE_SYMTAB NumWords=4 BlockCodeSize=4>
+;      <BBENTRY abbrevid=7 op0=0 op1=101 op2=110 op3=116 op4=114 op5=121/>
+;      <ENTRY abbrevid=6 op0=33 op1=115 op2=97 op3=121 op4=105 op5=110 op6=103/>
+;    </VALUE_SYMTAB>
+;  </FUNCTION_BLOCK>
+;  <FUNCTION_BLOCK NumWords=23 BlockCodeSize=4>
+;    <DECLAREBLOCKS op0=1/>
+;    <CONSTANTS_BLOCK NumWords=4 BlockCodeSize=4>
+;      <SETTYPE abbrevid=4 op0=1/>
+;      <CE_INBOUNDS_GEP op0=6 op1=4 op2=21 op3=18 op4=21 op5=18/>
+;      <CE_INBOUNDS_GEP op0=8 op1=5 op2=21 op3=18 op4=21 op5=18/>
+;    </CONSTANTS_BLOCK>
+;    <INST_LOAD op0=4294966291 op1=2 op2=0 op3=0/>
+;    <INST_CALL op0=0 op1=0 op2=24 op3=1 op4=3/>
+;    <INST_CAST abbrevid=7 op0=1 op1=15 op2=11/>
+;    <INST_LOAD abbrevid=4 op0=36 op1=0 op2=0/>
+;    <INST_CALL op0=0 op1=0 op2=27 op3=1 op4=5/>
+;    <INST_CAST abbrevid=7 op0=1 op1=17 op2=11/>
+;    <INST_CALL op0=0 op1=0 op2=1 op3=3/>
+;    <INST_CALL op0=0 op1=0 op2=5 op3=7 op4=1/>
+;    <INST_RET abbrevid=9 op0=1/>
+;    <VALUE_SYMTAB NumWords=2 BlockCodeSize=4>
+;      <BBENTRY abbrevid=7 op0=0 op1=101 op2=110 op3=116 op4=114 op5=121/>
+;    </VALUE_SYMTAB>
+;  </FUNCTION_BLOCK>
+;  <FUNCTION_BLOCK NumWords=15 BlockCodeSize=4>
+;    <DECLAREBLOCKS op0=1/>
+;    <CONSTANTS_BLOCK NumWords=3 BlockCodeSize=4>
+;      <SETTYPE abbrevid=4 op0=1/>
+;      <CE_INBOUNDS_GEP op0=10 op1=11 op2=21 op3=18 op4=21 op5=18/>
+;    </CONSTANTS_BLOCK>
+;    <INST_LOAD abbrevid=4 op0=23 op1=0 op2=0/>
+;    <INST_CALL op0=0 op1=0 op2=22 op3=1 op4=2/>
+;    <INST_CAST abbrevid=7 op0=1 op1=17 op2=11/>
+;    <INST_CALL op0=0 op1=0 op2=1 op3=3/>
+;    <INST_RET abbrevid=9 op0=19/>
+;    <VALUE_SYMTAB NumWords=2 BlockCodeSize=4>
+;      <BBENTRY abbrevid=7 op0=0 op1=101 op2=110 op3=116 op4=114 op5=121/>
+;    </VALUE_SYMTAB>
+;  </FUNCTION_BLOCK>
+;</MODULE_BLOCK>
diff --git a/test/Bitcode/pr18704.ll.bc b/test/Bitcode/pr18704.ll.bc
new file mode 100644
index 00000000000..dbfcf37b82a
Binary files /dev/null and b/test/Bitcode/pr18704.ll.bc differ