diff --git a/AST.cpp b/AST.cpp
index ee6e52250..05e2d52e8 100644
--- a/AST.cpp
+++ b/AST.cpp
@@ -784,8 +784,7 @@ void Expression::expectType(Type const& _expectedType)
 			" is not implicitly convertible to expected type " +
 			_expectedType.toString() +
 			"."
-		)
-		);
+		));
 }
 
 void Expression::requireLValue()
diff --git a/ExpressionCompiler.cpp b/ExpressionCompiler.cpp
index 786d386d9..f27cf5fe5 100644
--- a/ExpressionCompiler.cpp
+++ b/ExpressionCompiler.cpp
@@ -85,6 +85,10 @@ void ExpressionCompiler::appendStateVariableAccessor(VariableDeclaration const&
 		if (auto mappingType = dynamic_cast<MappingType const*>(returnType.get()))
 		{
 			solAssert(CompilerUtils::freeMemoryPointer >= 0x40, "");
+			solAssert(
+				!paramTypes[i]->isDynamicallySized(),
+				"Accessors for mapping with dynamically-sized keys not yet implemented."
+			);
 			// pop offset
 			m_context << eth::Instruction::POP;
 			// move storage offset to memory.
@@ -803,15 +807,30 @@ bool ExpressionCompiler::visit(IndexAccess const& _indexAccess)
 	if (baseType.getCategory() == Type::Category::Mapping)
 	{
 		// stack: storage_base_ref
-		Type const& keyType = *dynamic_cast<MappingType const&>(baseType).getKeyType();
-		m_context << u256(0); // memory position
+		auto const& mapping = dynamic_cast<MappingType const&>(baseType);
+		Type const& keyType = *mapping.getKeyType();
 		solAssert(_indexAccess.getIndexExpression(), "Index expression expected.");
-		solAssert(keyType.getCalldataEncodedSize() <= 0x20, "Dynamic keys not yet implemented.");
-		appendExpressionCopyToMemory(keyType, *_indexAccess.getIndexExpression());
-		m_context << eth::Instruction::SWAP1;
-		solAssert(CompilerUtils::freeMemoryPointer >= 0x40, "");
-		utils().storeInMemoryDynamic(IntegerType(256));
-		m_context << u256(0) << eth::Instruction::SHA3;
+		if (keyType.isDynamicallySized())
+		{
+			_indexAccess.getIndexExpression()->accept(*this);
+			utils().fetchFreeMemoryPointer();
+			// stack: base index mem
+			// note: the following operations must not allocate memory!
+			utils().encodeToMemory(TypePointers{mapping.getKeyType()}, TypePointers(), false, true);
+			m_context << eth::Instruction::SWAP1;
+			utils().storeInMemoryDynamic(IntegerType(256));
+			utils().toSizeAfterFreeMemoryPointer();
+		}
+		else
+		{
+			m_context << u256(0); // memory position
+			appendExpressionCopyToMemory(keyType, *_indexAccess.getIndexExpression());
+			m_context << eth::Instruction::SWAP1;
+			solAssert(CompilerUtils::freeMemoryPointer >= 0x40, "");
+			utils().storeInMemoryDynamic(IntegerType(256));
+			m_context << u256(0);
+		}
+		m_context << eth::Instruction::SHA3;
 		m_context << u256(0);
 		setLValueToStorageItem(_indexAccess);
 	}
diff --git a/Types.cpp b/Types.cpp
index d85c0511f..89ff2134f 100644
--- a/Types.cpp
+++ b/Types.cpp
@@ -179,6 +179,8 @@ TypePointer Type::fromMapping(ElementaryTypeName& _keyType, TypeName& _valueType
 		BOOST_THROW_EXCEPTION(_valueType.createTypeError("Invalid type name."));
 	// Convert value type to storage reference.
 	valueType = ReferenceType::copyForLocationIfReference(DataLocation::Storage, valueType);
+	// Convert key type to memory.
+	keyType = ReferenceType::copyForLocationIfReference(DataLocation::Memory, keyType);
 	return make_shared<MappingType>(keyType, valueType);
 }