diff --git a/executable_semantics/interpreter/type_checker.cpp b/executable_semantics/interpreter/type_checker.cpp
index 9a3681f7f282..5e43cc767236 100644
--- a/executable_semantics/interpreter/type_checker.cpp
+++ b/executable_semantics/interpreter/type_checker.cpp
@@ -1421,6 +1421,10 @@ void TypeChecker::DeclareDeclaration(Nonnull<Declaration*> d,
       auto& var = cast<VariableDeclaration>(*d);
       // Associate the variable name with it's declared type in the
       // compile-time symbol table.
+      if (!llvm::isa<ExpressionPattern>(var.binding().type())) {
+        FATAL_COMPILATION_ERROR(var.binding().type().source_loc())
+            << "Expected expression for variable type";
+      }
       Expression& type =
           cast<ExpressionPattern>(var.binding().type()).expression();
       TypeCheckPattern(&var.binding(), std::nullopt, impl_scope);
diff --git a/executable_semantics/syntax/lexer.lpp b/executable_semantics/syntax/lexer.lpp
index e282e77fe76e..462f1666d74b 100644
--- a/executable_semantics/syntax/lexer.lpp
+++ b/executable_semantics/syntax/lexer.lpp
@@ -266,8 +266,10 @@ string_literal        \"([^\\\"\n\v\f\r]|\\.)*\"
 
 {integer_literal} {
   BEGIN(AFTER_OPERAND);
-  int val;
-  CHECK(llvm::to_integer(yytext, val));
+  int val = 0;
+  if (!llvm::to_integer(yytext, val)) {
+    FATAL_SYNTAX_ERROR(context) << "Invalid integer literal: " << yytext;
+  }
   return ARG_TOKEN(integer_literal, val);
 }
 
diff --git a/executable_semantics/testdata/basic_syntax/fail_invalid_integer.carbon b/executable_semantics/testdata/basic_syntax/fail_invalid_integer.carbon
new file mode 100644
index 000000000000..0d2389a25a65
--- /dev/null
+++ b/executable_semantics/testdata/basic_syntax/fail_invalid_integer.carbon
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// RUN: %{not} %{executable_semantics} %s 2>&1 | \
+// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
+// RUN: %{not} %{executable_semantics} --trace %s 2>&1 | \
+// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// AUTOUPDATE: %{executable_semantics} %s
+// CHECK: COMPILATION ERROR: {{.*}}/executable_semantics/testdata/basic_syntax/fail_invalid_integer.carbon:15: Invalid integer literal: 11111111111111111111111111
+
+package ExecutableSemanticsTest api;
+
+fn Main() -> i32 {
+  return 11111111111111111111111111;
+}
diff --git a/executable_semantics/testdata/basic_syntax/fail_invalid_var_expression.carbon b/executable_semantics/testdata/basic_syntax/fail_invalid_var_expression.carbon
new file mode 100644
index 000000000000..dccd4f1ef803
--- /dev/null
+++ b/executable_semantics/testdata/basic_syntax/fail_invalid_var_expression.carbon
@@ -0,0 +1,16 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// RUN: %{not} %{executable_semantics} %s 2>&1 | \
+// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
+// RUN: %{not} %{executable_semantics} --trace %s 2>&1 | \
+// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// AUTOUPDATE: %{executable_semantics} %s
+// CHECK: COMPILATION ERROR: {{.*}}/executable_semantics/testdata/basic_syntax/fail_invalid_var_expression.carbon:14: Expected expression for variable type
+
+package ExecutableSemanticsTest api;
+
+var a: auto;
+
+fn Main() -> i32 { return 0; }