diff --git a/src/stdlib/__tests__/__snapshots__/misc.ts.snap b/src/stdlib/__tests__/__snapshots__/misc.ts.snap
new file mode 100644
index 000000000..9dcc40e83
--- /dev/null
+++ b/src/stdlib/__tests__/__snapshots__/misc.ts.snap
@@ -0,0 +1,62 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`parse_int with non-integer arg radix throws error 1`] = `
+Object {
+  "status": "error",
+}
+`;
+
+exports[`parse_int with non-integer arg radix throws error 2`] = `"Line 2: Error: parse_int expects two arguments a string s, and a positive integer i between 2 and 36, inclusive."`;
+
+exports[`parse_int with non-string arg str throws error 1`] = `
+Object {
+  "status": "error",
+}
+`;
+
+exports[`parse_int with non-string arg str throws error 2`] = `"Line 2: Error: parse_int expects two arguments a string s, and a positive integer i between 2 and 36, inclusive."`;
+
+exports[`parse_int with radix outside [2, 36] throws error, radix=1 1`] = `
+Object {
+  "status": "error",
+}
+`;
+
+exports[`parse_int with radix outside [2, 36] throws error, radix=1 2`] = `"Line 2: Error: parse_int expects two arguments a string s, and a positive integer i between 2 and 36, inclusive."`;
+
+exports[`parse_int with radix outside [2, 36] throws error, radix=37 1`] = `
+Object {
+  "status": "error",
+}
+`;
+
+exports[`parse_int with radix outside [2, 36] throws error, radix=37 2`] = `"Line 2: Error: parse_int expects two arguments a string s, and a positive integer i between 2 and 36, inclusive."`;
+
+exports[`parse_int with string arg radix throws error 1`] = `
+Object {
+  "status": "error",
+}
+`;
+
+exports[`parse_int with string arg radix throws error 2`] = `"Line 2: Error: parse_int expects two arguments a string s, and a positive integer i between 2 and 36, inclusive."`;
+
+exports[`parse_int with valid args is ok, but invalid str for radix 1`] = `
+Object {
+  "status": "finished",
+  "value": NaN,
+}
+`;
+
+exports[`parse_int with valid args is ok, radix 2 1`] = `
+Object {
+  "status": "finished",
+  "value": 6485,
+}
+`;
+
+exports[`parse_int with valid args is ok, radix 36 1`] = `
+Object {
+  "status": "finished",
+  "value": 39961,
+}
+`;
diff --git a/src/stdlib/__tests__/misc.ts b/src/stdlib/__tests__/misc.ts
new file mode 100644
index 000000000..496ba5abb
--- /dev/null
+++ b/src/stdlib/__tests__/misc.ts
@@ -0,0 +1,112 @@
+import { mockContext } from "../../mocks/context"
+import { parseError, runInContext } from "../../index"
+import { Finished } from "../../types";
+
+test("parse_int with valid args is ok, radix 2", () => {
+  const program = `
+    parse_int('1100101010101', 2);
+  `
+  const context = mockContext()
+  const promise = runInContext(program, context, { scheduler: "preemptive" })
+  return promise.then(obj => {
+    expect(obj).toMatchSnapshot()
+    expect(obj.status).toBe('finished')
+    expect((obj as Finished).value).toBe(parseInt('1100101010101', 2))
+  })
+})
+
+test("parse_int with valid args is ok, radix 36", () => {
+  const program = `
+    parse_int('uu1', 36);
+  `
+  const context = mockContext()
+  const promise = runInContext(program, context, { scheduler: "preemptive" })
+  return promise.then(obj => {
+    expect(obj).toMatchSnapshot()
+    expect(obj.status).toBe('finished')
+    expect((obj as Finished).value).toBe(parseInt('uu1', 36))
+  })
+})
+
+test("parse_int with valid args is ok, but invalid str for radix", () => {
+  const program = `
+    parse_int('uu1', 2);
+  `
+  const context = mockContext()
+  const promise = runInContext(program, context, { scheduler: "preemptive" })
+  return promise.then(obj => {
+    expect(obj).toMatchSnapshot()
+    expect(obj.status).toBe('finished')
+    expect((obj as Finished).value).toBe(parseInt('uu1', 2))
+  })
+})
+
+test("parse_int with non-string arg str throws error", () => {
+  const program = `
+    parse_int(42, 2);
+  `
+  const context = mockContext()
+  const promise = runInContext(program, context, { scheduler: "preemptive" })
+  return promise.then(obj => {
+    expect(obj).toMatchSnapshot()
+    expect(obj.status).toBe('error')
+    const errors = parseError(context.errors)
+    expect(errors).toMatchSnapshot()
+  })
+})
+
+test("parse_int with non-integer arg radix throws error", () => {
+  const program = `
+    parse_int(42, 2.1);
+  `
+  const context = mockContext()
+  const promise = runInContext(program, context, { scheduler: "preemptive" })
+  return promise.then(obj => {
+    expect(obj).toMatchSnapshot()
+    expect(obj.status).toBe('error')
+    const errors = parseError(context.errors)
+    expect(errors).toMatchSnapshot()
+  })
+})
+
+test("parse_int with radix outside [2, 36] throws error, radix=1", () => {
+  const program = `
+    parse_int('10', 1);
+  `
+  const context = mockContext()
+  const promise = runInContext(program, context, { scheduler: "preemptive" })
+  return promise.then(obj => {
+    expect(obj).toMatchSnapshot()
+    expect(obj.status).toBe('error')
+    const errors = parseError(context.errors)
+    expect(errors).toMatchSnapshot()
+  })
+})
+
+test("parse_int with radix outside [2, 36] throws error, radix=37", () => {
+  const program = `
+    parse_int('10', 37);
+  `
+  const context = mockContext()
+  const promise = runInContext(program, context, { scheduler: "preemptive" })
+  return promise.then(obj => {
+    expect(obj).toMatchSnapshot()
+    expect(obj.status).toBe('error')
+    const errors = parseError(context.errors)
+    expect(errors).toMatchSnapshot()
+  })
+})
+
+test("parse_int with string arg radix throws error", () => {
+  const program = `
+    parse_int(42, '2');
+  `
+  const context = mockContext()
+  const promise = runInContext(program, context, { scheduler: "preemptive" })
+  return promise.then(obj => {
+    expect(obj).toMatchSnapshot()
+    expect(obj.status).toBe('error')
+    const errors = parseError(context.errors)
+    expect(errors).toMatchSnapshot()
+  })
+})
diff --git a/src/stdlib/misc.ts b/src/stdlib/misc.ts
index 536864d0d..6041dd1e2 100644
--- a/src/stdlib/misc.ts
+++ b/src/stdlib/misc.ts
@@ -43,13 +43,20 @@ export function array_length(xs: Value[]) {
 }
 array_length.__SOURCE__ = 'array_length(xs)'
 
-export function parse_int(inputString: string, radix: number) {
-  const parsed = parseInt(inputString, radix)
-  if (inputString && radix && parsed) {
-    // the two arguments are provided, and parsed is not NaN
-    return parsed
+/**
+ * Source version of parseInt. Both arguments are required.
+ *
+ * @param str String representation of the integer to be parsed. Required.
+ * @param radix Base to parse the given `str`. Required.
+ *
+ * An error is thrown if `str` is not of type string, or `radix` is not an
+ * integer within the range 2, 36 inclusive.
+ */
+export function parse_int(str: string, radix: number) {
+  if (typeof(str) === 'string' && typeof(radix) === 'number' && Number.isInteger(radix) && 2 <= radix && radix <= 36) {
+    return parseInt(str, radix)
   } else {
-    throw new Error('parse_int expects two arguments a string s, and a positive integer i')
+    throw new Error('parse_int expects two arguments a string s, and a positive integer i between 2 and 36, inclusive.')
   }
 }
 parse_int.__SOURCE__ = 'parse_int(s, i)'