diff --git a/.travis.yml b/.travis.yml
index d62fb96..f836273 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,7 +5,7 @@ matrix:
   include:
   - os: osx
     language: objective-c
-    osx_image: xcode10
+    osx_image: xcode10.2
     script:
     - swift test
   - os: linux
@@ -15,9 +15,9 @@ matrix:
     env:
     before_install:
     - wget -q -O - https://swift.org/keys/all-keys.asc | gpg --import -
-    - wget https://swift.org/builds/swift-4.2-release/ubuntu1404/swift-4.2-RELEASE/swift-4.2-RELEASE-ubuntu14.04.tar.gz
-    - tar xzf swift-4.2-RELEASE-ubuntu14.04.tar.gz
-    - export PATH=${PWD}/swift-4.2-RELEASE-ubuntu14.04/usr/bin:"${PATH}"
+    - wget https://swift.org/builds/swift-5.0-release/ubuntu1404/swift-5.0-RELEASE/swift-5.0-RELEASE-ubuntu14.04.tar.gz
+    - tar xzf swift-5.0-RELEASE-ubuntu14.04.tar.gz
+    - export PATH=${PWD}/swift-5.0-RELEASE-ubuntu14.04/usr/bin:"${PATH}"
     script:
     - swift test
 notifications:
diff --git a/Package.swift b/Package.swift
index 7271bc1..5875de6 100644
--- a/Package.swift
+++ b/Package.swift
@@ -1,4 +1,4 @@
-// swift-tools-version:4.2
+// swift-tools-version:5.0
 
 import PackageDescription
 
diff --git a/Sources/FileCheck/FileCheck.swift b/Sources/FileCheck/FileCheck.swift
index f8ce16c..18ff40c 100644
--- a/Sources/FileCheck/FileCheck.swift
+++ b/Sources/FileCheck/FileCheck.swift
@@ -442,15 +442,15 @@ private func readCheckStrings(in buf : UnsafeBufferPointer<CChar>, withPrefixes
     // Okay, we found the prefix, yay. Remember the rest of the line, but
     // ignore leading whitespace.
     if !options.contains(.strictWhitespace) || !options.contains(.matchFullLines) {
-      guard let idx = buffer.index(where: { c in c != (" " as Character).utf8CodePoint && c != ("\t" as Character).utf8CodePoint }) else {
+      guard let idx = buffer.firstIndex(where: { c in c != (" " as Character).utf8CodePoint && c != ("\t" as Character).utf8CodePoint }) else {
         return []
       }
       buffer = buffer.dropFront(idx)
     }
 
     // Scan ahead to the end of line.
-    let EOL : Int = buffer.index(of: ("\n" as Character).utf8CodePoint)
-                  ?? buffer.index(of: ("\r" as Character).utf8CodePoint)
+    let EOL : Int = buffer.firstIndex(of: ("\n" as Character).utf8CodePoint)
+                  ?? buffer.firstIndex(of: ("\r" as Character).utf8CodePoint)
                   ?? buffer.count - 1
 
     // Remember the location of the start of the pattern, for diagnostics.
diff --git a/Sources/FileCheck/Pattern.swift b/Sources/FileCheck/Pattern.swift
index e23cad7..2f038b0 100644
--- a/Sources/FileCheck/Pattern.swift
+++ b/Sources/FileCheck/Pattern.swift
@@ -447,7 +447,7 @@ func countNewlines(in str : String) -> (count: Int, firstIndex: String.Index?) {
     // Scan for newline.
 
     // If we can't find a newline, bail.
-    guard let EOL = range.index(of: "\n") ?? range.index(of: "\r") else {
+    guard let EOL = range.firstIndex(of: "\n") ?? range.firstIndex(of: "\r") else {
       return (newlineCount, firstNewLine)
     }