diff --git a/SPIRV/GlslangToSpv.cpp b/SPIRV/GlslangToSpv.cpp
index 86e6ac3..90cb2c0 100755
--- a/SPIRV/GlslangToSpv.cpp
+++ b/SPIRV/GlslangToSpv.cpp
@@ -741,11 +741,12 @@
 
         // Normal .length() would have been constant folded by the front-end.
         // So, this has to be block.lastMember.length().
-        // SPV wants "block" as the operand, go get it.
+        // SPV wants "block" and member number as the operands, go get them.
         assert(node->getOperand()->getType().isRuntimeSizedArray());
         glslang::TIntermTyped* block = node->getOperand()->getAsBinaryNode()->getLeft();
         block->traverse(this);
-        spv::Id length = builder.createUnaryOp(spv::OpArrayLength, builder.makeIntType(32), builder.accessChainGetLValue());
+        unsigned int member = node->getOperand()->getAsBinaryNode()->getRight()->getAsConstantUnion()->getConstArray()[0].getUConst();
+        spv::Id length = builder.createArrayLength(builder.accessChainGetLValue(), member);
 
         builder.clearAccessChain();
         builder.setAccessChainRValue(length);
diff --git a/SPIRV/SpvBuilder.cpp b/SPIRV/SpvBuilder.cpp
index 9d8288a..8b209b6 100755
--- a/SPIRV/SpvBuilder.cpp
+++ b/SPIRV/SpvBuilder.cpp
@@ -890,6 +890,16 @@
     return chain->getResultId();
 }
 
+Id Builder::createArrayLength(Id base, unsigned int member)
+{
+    Instruction* length = new Instruction(getUniqueId(), makeIntType(32), OpArrayLength);
+    length->addIdOperand(base);
+    length->addImmediateOperand(member);
+    buildPoint->addInstruction(length);
+
+    return length->getResultId();
+}
+
 Id Builder::createCompositeExtract(Id composite, Id typeId, unsigned index)
 {
     Instruction* extract = new Instruction(getUniqueId(), typeId, OpCompositeExtract);
diff --git a/SPIRV/SpvBuilder.h b/SPIRV/SpvBuilder.h
index 23b9bc2..1a6be6a 100755
--- a/SPIRV/SpvBuilder.h
+++ b/SPIRV/SpvBuilder.h
@@ -225,6 +225,9 @@
     // Create an OpAccessChain instruction
     Id createAccessChain(StorageClass, Id base, std::vector<Id>& offsets);
 
+    // Create an OpArrayLength instruction
+    Id createArrayLength(Id base, unsigned int member);
+
     // Create an OpCompositeExtract instruction
     Id createCompositeExtract(Id composite, Id typeId, unsigned index);
     Id createCompositeExtract(Id composite, Id typeId, std::vector<unsigned>& indexes);