diff --git a/src/datatypes/compiler-utils.js b/src/datatypes/compiler-utils.js
index 2c3d5a8..d60eda5 100644
--- a/src/datatypes/compiler-utils.js
+++ b/src/datatypes/compiler-utils.js
@@ -159,7 +159,9 @@ return (ctx.${type})(val, buffer, offset)
     }],
     mapper: ['parametrizable', (compiler, mapper) => {
       const mappings = JSON.stringify(swapMappings(mapper.mappings))
-      const code = 'return ' + compiler.callType(`${mappings}[value] || value`, mapper.type)
+      let code = `const mapped = ${mappings}[value]\n`
+      code += 'if (mapped === undefined) throw new Error(value + \' is not in the mappings value\')\n'
+      code += 'return ' + compiler.callType('mapped', mapper.type)
       return compiler.wrapCode(code)
     }]
   },
@@ -211,7 +213,9 @@ return (ctx.${type})(val)
     }],
     mapper: ['parametrizable', (compiler, mapper) => {
       const mappings = JSON.stringify(swapMappings(mapper.mappings))
-      const code = 'return ' + compiler.callType(`${mappings}[value] || value`, mapper.type)
+      let code = `const mapped = ${mappings}[value]\n`
+      code += 'if (mapped === undefined) throw new Error(value + \' is not in the mappings value\')\n'
+      code += 'return ' + compiler.callType('mapped', mapper.type)
       return compiler.wrapCode(code)
     }]
   }
diff --git a/test/misc.js b/test/misc.js
index 83200bc..dab6359 100644
--- a/test/misc.js
+++ b/test/misc.js
@@ -1,5 +1,27 @@
 /* eslint-env mocha */
 
+const assert = require('assert')
+const { ProtoDef } = require('../')
+const { ProtoDefCompiler } = require('../').Compiler
+
 it('example works', () => {
   require('../example')
 })
+
+describe('mapper', () => {
+  const mapper = ['mapper', { type: 'varint', mappings: { '0x00': 'zero', '0x01': 'one' } }]
+  const proto = new ProtoDef()
+  proto.addType('name', mapper)
+  const compiler = new ProtoDefCompiler()
+  compiler.addTypesToCompile({ name: mapper })
+  const compiled = compiler.compileProtoDefSync()
+
+  for (const [label, p] of [['interpreted', proto], ['compiled', compiled]]) {
+    it(`writes a value mapped to 0 (${label})`, () => {
+      assert.deepStrictEqual(p.createPacketBuffer('name', 'zero'), Buffer.from([0]))
+    })
+    it(`throws on a value not in the mappings instead of writing it (${label})`, () => {
+      assert.throws(() => p.createPacketBuffer('name', 'nope'), /nope is not in the mappings value/)
+    })
+  }
+})