diff --git a/.travis.yml b/.travis.yml
index c45fd401..2356cd12 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -7,6 +7,7 @@ os:
 
 go:
   - "1.12.x"
+  - "1.13.x"
 
 before_script:
 - go get -u 
diff --git a/Dockerfile b/Dockerfile
index 49d521ae..cce804a6 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM golang:1.12
+FROM golang:1.13
 
 RUN apt-get update
 RUN apt-get install bash make git curl jq -y
diff --git a/docs/misc/technical-details.md b/docs/misc/technical-details.md
index 019ca28e..9dcca02d 100644
--- a/docs/misc/technical-details.md
+++ b/docs/misc/technical-details.md
@@ -1,6 +1,6 @@
 # A few technical details...
 
-The ABS interpreter is built with Golang version `1.11`, and is mostly based on [the interpreter book](https://interpreterbook.com/) written by [Thorsten Ball](https://twitter.com/thorstenball).
+The ABS interpreter is built with Golang version `1.13`, and is mostly based on [the interpreter book](https://interpreterbook.com/) written by [Thorsten Ball](https://twitter.com/thorstenball).
 
 ABS is extremely different from Monkey, the "fictional" language the reader builds throughout the book, but the base structure (lexer, parser, evaluator) are still very much based on Thorsten's work.
 
diff --git a/evaluator/evaluator_test.go b/evaluator/evaluator_test.go
index c322c477..cc0d760c 100644
--- a/evaluator/evaluator_test.go
+++ b/evaluator/evaluator_test.go
@@ -802,7 +802,7 @@ func TestBuiltinFunctions(t *testing.T) {
 		{`find([1,2,3,3], f(x) {x == 3})`, 3},
 		{`find([1,2], f(x) {x == "some"})`, nil},
 		{`arg("o")`, "argument 0 to arg(...) is not supported (got: o, allowed: NUMBER)"},
-		{`arg(3)`, ""},
+		{`arg(99)`, ""},
 		{`pwd().split("").reverse().slice(0, 33).reverse().join("").replace("\\", "/", -1).suffix("/evaluator")`, true}, // Little trick to get travis to run this test, as the base path is not /go/src/
 		{`cwd = cd(); cwd == pwd()`, true},
 		{`cwd = cd("path/to/nowhere"); cwd == pwd()`, false},