diff --git a/Changelog.md b/Changelog.md
index 30bb94742..567c13b1b 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -34,6 +34,7 @@ Bugfixes:
  * SMTChecker: Fix internal error when assigning to a 1-tuple.
  * State Mutability: Constant public state variables are considered ``pure`` functions.
  * Type Checker: Fixing deduction issues on function types when function call has named arguments.
+ * Immutables: Fix internal compiler error when immutables are not assigned.
 
 
 ### 0.6.12 (2020-07-22)
diff --git a/libevmasm/Assembly.cpp b/libevmasm/Assembly.cpp
index b1de71e3b..c729a4eb4 100644
--- a/libevmasm/Assembly.cpp
+++ b/libevmasm/Assembly.cpp
@@ -30,6 +30,8 @@
 #include <libevmasm/ConstantOptimiser.h>
 #include <libevmasm/GasMeter.h>
 
+#include <liblangutil/Exceptions.h>
+
 #include <fstream>
 #include <json/json.h>
 
@@ -699,12 +701,10 @@ LinkerObject const& Assembly::assemble() const
 		}
 	}
 
-	assertThrow(
-		immutableReferencesBySub.empty(),
-		AssemblyException,
-		"Some immutables were read from but never assigned."
-	);
-
+	if (!immutableReferencesBySub.empty())
+		throw
+			langutil::Error(1284_error, langutil::Error::Type::CodeGenerationError) <<
+			util::errinfo_comment("Some immutables were read from but never assigned, possibly because of optimization.");
 
 	if (!m_subs.empty() || !m_data.empty() || !m_auxiliaryData.empty())
 		// Append an INVALID here to help tests find miscompilation.
diff --git a/liblangutil/Exceptions.cpp b/liblangutil/Exceptions.cpp
index 2e9d22b41..0661d5ce5 100644
--- a/liblangutil/Exceptions.cpp
+++ b/liblangutil/Exceptions.cpp
@@ -33,6 +33,9 @@ Error::Error(ErrorId _errorId, Type _type, SourceLocation const& _location, stri
 {
 	switch (m_type)
 	{
+	case Type::CodeGenerationError:
+		m_typeName = "CodeGenerationError";
+		break;
 	case Type::DeclarationError:
 		m_typeName = "DeclarationError";
 		break;
diff --git a/liblangutil/Exceptions.h b/liblangutil/Exceptions.h
index 69745a2fc..29acb7ee4 100644
--- a/liblangutil/Exceptions.h
+++ b/liblangutil/Exceptions.h
@@ -78,6 +78,7 @@ class Error: virtual public util::Exception
 public:
 	enum class Type
 	{
+		CodeGenerationError,
 		DeclarationError,
 		DocstringParsingError,
 		ParserError,
diff --git a/libsolidity/interface/CompilerStack.cpp b/libsolidity/interface/CompilerStack.cpp
index 27a51552e..41a9040c4 100644
--- a/libsolidity/interface/CompilerStack.cpp
+++ b/libsolidity/interface/CompilerStack.cpp
@@ -516,7 +516,17 @@ bool CompilerStack::compile()
 			if (auto contract = dynamic_cast<ContractDefinition const*>(node.get()))
 				if (isRequestedContract(*contract))
 				{
-					compileContract(*contract, otherCompilers);
+					try
+					{
+						compileContract(*contract, otherCompilers);
+					}
+					catch (Error const& _error)
+					{
+						if (_error.type() != Error::Type::CodeGenerationError)
+							throw;
+						m_errorReporter.error(_error.errorId(), _error.type(), SourceLocation(), _error.what());
+						return false;
+					}
 					if (m_generateIR || m_generateEwasm)
 						generateIR(*contract);
 					if (m_generateEwasm)
diff --git a/test/libsolidity/SyntaxTest.cpp b/test/libsolidity/SyntaxTest.cpp
index c554366e9..92b246b34 100644
--- a/test/libsolidity/SyntaxTest.cpp
+++ b/test/libsolidity/SyntaxTest.cpp
@@ -74,7 +74,19 @@ void SyntaxTest::parseAndAnalyze()
 		try
 		{
 			if (!compiler().compile())
-				BOOST_THROW_EXCEPTION(runtime_error("Compilation failed even though analysis was successful."));
+			{
+				ErrorList const& errors = compiler().errors();
+				auto codeGeneretionErrorCount = count_if(errors.cbegin(), errors.cend(), [](auto const& error) {
+					return error->type() == Error::Type::CodeGenerationError;
+				});
+				auto errorCount = count_if(errors.cbegin(), errors.cend(), [](auto const& error) {
+					return error->type() != Error::Type::Warning;
+				});
+				// failing compilation after successful analysis is a rare case,
+				// it assumes that errors contain exactly one error, and the error is of type Error::Type::CodeGenerationError
+				if (codeGeneretionErrorCount != 1 || errorCount != 1)
+					BOOST_THROW_EXCEPTION(runtime_error("Compilation failed even though analysis was successful."));
+			}
 		}
 		catch (UnimplementedFeatureError const& _e)
 		{
diff --git a/test/libsolidity/syntaxTests/immutable/no_assignments.sol b/test/libsolidity/syntaxTests/immutable/no_assignments.sol
new file mode 100644
index 000000000..7357d174a
--- /dev/null
+++ b/test/libsolidity/syntaxTests/immutable/no_assignments.sol
@@ -0,0 +1,13 @@
+contract C {
+    uint immutable x;
+    constructor() {
+        x = 0;
+        while (true)
+        {}
+    }
+    function f() external view returns(uint) { return x; }
+}
+// ====
+// optimize-yul: true
+// ----
+// CodeGenerationError 1284: Some immutables were read from but never assigned, possibly because of optimization.