diff --git a/package.json b/package.json
index 9c5c26885..b29be012b 100644
--- a/package.json
+++ b/package.json
@@ -91,7 +91,7 @@
     "deprecation-cop": "0.53.0",
     "dev-live-reload": "0.46.0",
     "encoding-selector": "0.21.0",
-    "exception-reporting": "0.34.0",
+    "exception-reporting": "0.35.0",
     "find-and-replace": "0.174.2",
     "fuzzy-finder": "0.87.0",
     "git-diff": "0.55.0",
diff --git a/spec/atom-spec.coffee b/spec/atom-spec.coffee
index d2d1d68ae..13b62c8e3 100644
--- a/spec/atom-spec.coffee
+++ b/spec/atom-spec.coffee
@@ -127,7 +127,7 @@ describe "the `atom` global", ->
           column: 3
           originalError: error
 
-  describe ".assert(condition, message, metadata)", ->
+  describe ".assert(condition, message, callback)", ->
     errors = null
 
     beforeEach ->
@@ -142,17 +142,11 @@ describe "the `atom` global", ->
         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 passed a callback function", ->
+        it "calls the callback with the assertion failure's error object", ->
+          error = null
+          atom.assert(false, "a == b", (e) -> error = e)
+          expect(error).toBe errors[0]
 
     describe "if the condition is true", ->
       it "does nothing", ->
diff --git a/src/atom.coffee b/src/atom.coffee
index 03525df68..d50c49a30 100644
--- a/src/atom.coffee
+++ b/src/atom.coffee
@@ -721,17 +721,12 @@ class Atom extends Model
   Section: Private
   ###
 
-  assert: (condition, message, metadata) ->
+  assert: (condition, message, callback) ->
     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
+    callback?(error)
 
     @emitter.emit 'did-fail-assertion', error
 
diff --git a/src/lines-tile-component.coffee b/src/lines-tile-component.coffee
index 5fdadf212..8af408da5 100644
--- a/src/lines-tile-component.coffee
+++ b/src/lines-tile-component.coffee
@@ -346,17 +346,44 @@ class LinesTileComponent
             rangeForMeasurement ?= document.createRange()
             iterator =  document.createNodeIterator(lineNode, NodeFilter.SHOW_TEXT, AcceptFilter)
             textNode = iterator.nextNode()
+            textNodeLength = textNode.length
             textNodeIndex = 0
             nextTextNodeIndex = textNode.textContent.length
 
           while nextTextNodeIndex <= charIndex
             textNode = iterator.nextNode()
+            textNodeLength = textNode.length
             textNodeIndex = nextTextNodeIndex
             nextTextNodeIndex = textNodeIndex + textNode.textContent.length
 
           i = charIndex - textNodeIndex
           rangeForMeasurement.setStart(textNode, i)
-          rangeForMeasurement.setEnd(textNode, i + charLength)
+
+          if i + charLength <= textNodeLength
+            rangeForMeasurement.setEnd(textNode, i + charLength)
+          else
+            rangeForMeasurement.setEnd(textNode, textNodeLength)
+            atom.assert false, "Expected index to be less than the length of text node while measuring", (error) =>
+              editor = @presenter.model
+              screenRow = tokenizedLine.screenRow
+              bufferRow = editor.bufferRowForScreenRow(screenRow)
+
+              error.metadata = {
+                grammarScopeName: editor.getGrammar().scopeName
+                screenRow: screenRow
+                bufferRow: bufferRow
+                softWrapped: editor.isSoftWrapped()
+                softTabs: editor.getSoftTabs()
+                i: i
+                charLength: charLength
+                textNodeLength: textNode.length
+              }
+              error.privateMetadataDescription = "The contents of line #{bufferRow + 1}."
+              error.privateMetadata = {
+                lineText: editor.lineTextForBufferRow(bufferRow)
+              }
+              error.privateMetadataRequestName = "measured-line-text"
+
           charWidth = rangeForMeasurement.getBoundingClientRect().width
           @presenter.setScopedCharacterWidth(scopes, char, charWidth)
 
diff --git a/src/tokenized-buffer.coffee b/src/tokenized-buffer.coffee
index b662de08a..9c25e9cb3 100644
--- a/src/tokenized-buffer.coffee
+++ b/src/tokenized-buffer.coffee
@@ -296,10 +296,12 @@ class TokenizedBuffer extends Model
     # 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:
+    atom.assert tokenizedLine?, "TokenizedLine is defined", (error) =>
+      error.metadata = {
         row: row
         rowCount: @tokenizedLines.length
+      }
+
     return false unless tokenizedLine?
 
     return false if @buffer.isRowBlank(row) or tokenizedLine.isComment()