diff --git a/package.json b/package.json
index 8cca44bf7..fa8844a92 100644
--- a/package.json
+++ b/package.json
@@ -91,7 +91,7 @@
     "deprecation-cop": "0.53.0",
     "dev-live-reload": "0.46.0",
     "encoding-selector": "0.20.0",
-    "exception-reporting": "0.25.0",
+    "exception-reporting": "0.31.0",
     "find-and-replace": "0.174.1",
     "fuzzy-finder": "0.87.0",
     "git-diff": "0.55.0",
@@ -103,7 +103,7 @@
     "link": "0.30.0",
     "markdown-preview": "0.150.0",
     "metrics": "0.51.0",
-    "notifications": "0.56.0",
+    "notifications": "0.57.0",
     "open-on-github": "0.37.0",
     "package-generator": "0.39.0",
     "release-notes": "0.53.0",
diff --git a/spec/atom-spec.coffee b/spec/atom-spec.coffee
index 99a7f432e..d2d1d68ae 100644
--- a/spec/atom-spec.coffee
+++ b/spec/atom-spec.coffee
@@ -127,6 +127,39 @@ describe "the `atom` global", ->
           column: 3
           originalError: error
 
+  describe ".assert(condition, message, metadata)", ->
+    errors = null
+
+    beforeEach ->
+      errors = []
+      atom.onDidFailAssertion (error) -> errors.push(error)
+
+    describe "if the condition is false", ->
+      it "notifies onDidFailAssertion handlers with an error object based on the call site of the assertion", ->
+        result = atom.assert(false, "a == b")
+        expect(result).toBe false
+        expect(errors.length).toBe 1
+        expect(errors[0].message).toBe "Assertion failed: a == b"
+        expect(errors[0].stack).toContain('atom-spec')
+
+      describe "if metadata is an object", ->
+        it "assigns the object on the error as `metadata`", ->
+          metadata = {foo: 'bar'}
+          atom.assert(false, "a == b", metadata)
+          expect(errors[0].metadata).toBe metadata
+
+      describe "if metadata is a function", ->
+        it "assigns the function's return value on the error as `metadata`", ->
+          metadata = {foo: 'bar'}
+          atom.assert(false, "a == b", -> metadata)
+          expect(errors[0].metadata).toBe metadata
+
+    describe "if the condition is true", ->
+      it "does nothing", ->
+        result = atom.assert(true, "a == b")
+        expect(result).toBe true
+        expect(errors).toEqual []
+
   describe "saving and loading", ->
     afterEach -> atom.mode = "spec"
 
diff --git a/src/atom.coffee b/src/atom.coffee
index 316c51e29..03525df68 100644
--- a/src/atom.coffee
+++ b/src/atom.coffee
@@ -333,6 +333,12 @@ class Atom extends Model
   onDidThrowError: (callback) ->
     @emitter.on 'did-throw-error', callback
 
+  # TODO: Make this part of the public API. We should make onDidThrowError
+  # match the interface by only yielding an exception object to the handler
+  # and deprecating the old behavior.
+  onDidFailAssertion: (callback) ->
+    @emitter.on 'did-fail-assertion', callback
+
   ###
   Section: Atom Details
   ###
@@ -715,6 +721,22 @@ class Atom extends Model
   Section: Private
   ###
 
+  assert: (condition, message, metadata) ->
+    return true if condition
+
+    error = new Error("Assertion failed: #{message}")
+    Error.captureStackTrace(error, @assert)
+
+    if metadata?
+      if typeof metadata is 'function'
+        error.metadata = metadata()
+      else
+        error.metadata = metadata
+
+    @emitter.emit 'did-fail-assertion', error
+
+    false
+
   deserializeProject: ->
     Project = require './project'
 
diff --git a/src/tokenized-buffer.coffee b/src/tokenized-buffer.coffee
index c764c1a1f..5919841f5 100644
--- a/src/tokenized-buffer.coffee
+++ b/src/tokenized-buffer.coffee
@@ -292,7 +292,17 @@ class TokenizedBuffer extends Model
   # Returns a {Boolean} indicating whether the given buffer row starts
   # a a foldable row range due to the code's indentation patterns.
   isFoldableCodeAtRow: (row) ->
-    return false if @buffer.isRowBlank(row) or @tokenizedLineForRow(row).isComment()
+    # Investigating an exception that's occurring here due to the line being
+    # undefined. This should paper over the problem but we want to figure out
+    # what is happening:
+    tokenizedLine = @tokenizedLineForRow(row)
+    atom.assert tokenizedLine?, "TokenizedLine is defined", =>
+      metadata:
+        row: row
+        rowCount: @tokenizedLines.length
+    return false unless tokenizedLine?
+
+    return false if @buffer.isRowBlank(row) or tokenizedLine.isComment()
     nextRow = @buffer.nextNonBlankRow(row)
     return false unless nextRow?