diff --git a/lib/BattlePlan.js b/lib/BattlePlan.js
index abfda09..a02ac45 100644
--- a/lib/BattlePlan.js
+++ b/lib/BattlePlan.js
@@ -3,6 +3,8 @@
 module.exports = class BattlePlan {
 
   constructor(opts) {
+    validateOptions(opts)
+
     this.allocations = opts.allocations
     this.name = opts.name
     this.author = opts.author
@@ -37,3 +39,16 @@ module.exports = class BattlePlan {
     }
   }
 }
+
+function validateOptions(opts) {
+  if (!Array.isArray(opts.allocations)) {
+    throw new Error("a new BattlePlan's 'allocations' option must be an array")
+  }
+  if (opts.allocations.length !== 10) {
+    throw new Error(`A BattlePlan must allocate armies to exactly 10 castles, not ${opts.allocations.length}`)
+  }
+  const allocationSum = opts.allocations.reduce((acc, val) => acc + val, 0)
+  if (allocationSum !== 100) {
+    throw new Error(`A BattlePlan must allocate exactly 100 armies, not ${allocationSum}`)
+  }
+}
diff --git a/lib/BattlePlanSpec.js b/lib/BattlePlanSpec.js
index 2dab06c..2adc3ca 100644
--- a/lib/BattlePlanSpec.js
+++ b/lib/BattlePlanSpec.js
@@ -18,6 +18,39 @@ test('BattlePlan(opts) sets properties from options', function* (t) {
   t.is(myPlan.author, 'Genghis Khan')
 })
 
+test('throws an Error if opts.allocations is not an Array', function* (t) {
+  const err = t.throws(() => {
+    new BattlePlan({ // eslint-disable-line no-new
+      allocations: null,
+      name: 'test-plan',
+      author: 'Genghis Khan'
+    })
+  })
+  t.is(err.message, "a new BattlePlan's 'allocations' option must be an array")
+})
+
+test('allocations must include exactly 10 castles', function* (t) {
+  const err = t.throws(() => {
+    new BattlePlan({ // eslint-disable-line no-new
+      allocations: [20, 20, 20, 20, 20],
+      name: 'test-plan',
+      author: 'Genghis Khan'
+    })
+  })
+  t.is(err.message, 'A BattlePlan must allocate armies to exactly 10 castles, not 5')
+})
+
+test('allocations must total exactly 100', function* (t) {
+  const err = t.throws(() => {
+    new BattlePlan({ // eslint-disable-line no-new
+      allocations: [1, 1, 1, 1, 1, 1, 1, 1, 1, 1],
+      name: 'test-plan',
+      author: 'Genghis Khan'
+    })
+  })
+  t.is(err.message, 'A BattlePlan must allocate exactly 100 armies, not 10')
+})
+
 test('.fight(opponent) returns `win` when the first plan wins', function* (t) {
   t.is(samples.allToCastleTen.fight(samples.allToCastleOne), 'win')
 })