diff --git a/Cargo.lock b/Cargo.lock
index db3ff5619e..62df3a1332 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -117,6 +117,7 @@ dependencies = [
  "maplit 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "petgraph 0.4.13 (registry+https://github.com/rust-lang/crates.io-index)",
  "pretty_assertions 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "smallvec 0.6.9 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -148,6 +149,11 @@ dependencies = [
  "typenum 1.10.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "smallvec"
+version = "0.6.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "typenum"
 version = "1.10.0"
@@ -206,6 +212,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1d7eb9ef2c18661902cc47e535f9bc51b78acd254da71d375c2f6720d9a40403"
 "checksum semver-parser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
 "checksum sized-chunks 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "a2a2eb3fe454976eefb479f78f9b394d34d661b647c6326a3a6e66f68bb12c26"
+"checksum smallvec 0.6.9 (registry+https://github.com/rust-lang/crates.io-index)" = "c4488ae950c49d403731982257768f48fada354a5203fe81f9bb6f43ca9002be"
 "checksum typenum 1.10.0 (registry+https://github.com/rust-lang/crates.io-index)" = "612d636f949607bdf9b123b4a6f6d966dedf3ff669f7f045890d3a4a73948169"
 "checksum unreachable 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "382810877fe448991dfc7f0dd6e3ae5d58088fd0ea5e35189655f84e6814fa56"
 "checksum void 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "6a02e4885ed3bc0f2de90ea6dd45ebcbb66dacffe03547fadbb0eeae2770887d"
diff --git a/Cargo.toml b/Cargo.toml
index 0a4232714b..24bcf3c518 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,6 +9,7 @@ log = "0.4"
 petgraph = { version = "0.4.5", optional = true }
 combine = "3.8.1"
 im-rc = "13.0.0"
+smallvec = "0.6.9"
 
 [dev-dependencies]
 pretty_assertions = "0.5.1"
diff --git a/cli/Cargo.lock b/cli/Cargo.lock
index 11e7ec7923..537f080af2 100644
--- a/cli/Cargo.lock
+++ b/cli/Cargo.lock
@@ -62,6 +62,7 @@ dependencies = [
  "combine 3.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "im-rc 13.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "smallvec 0.6.9 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -100,6 +101,11 @@ dependencies = [
  "typenum 1.10.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "smallvec"
+version = "0.6.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "typenum"
 version = "1.10.0"
@@ -131,6 +137,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1d7eb9ef2c18661902cc47e535f9bc51b78acd254da71d375c2f6720d9a40403"
 "checksum semver-parser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
 "checksum sized-chunks 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "a2a2eb3fe454976eefb479f78f9b394d34d661b647c6326a3a6e66f68bb12c26"
+"checksum smallvec 0.6.9 (registry+https://github.com/rust-lang/crates.io-index)" = "c4488ae950c49d403731982257768f48fada354a5203fe81f9bb6f43ca9002be"
 "checksum typenum 1.10.0 (registry+https://github.com/rust-lang/crates.io-index)" = "612d636f949607bdf9b123b4a6f6d966dedf3ff669f7f045890d3a4a73948169"
 "checksum unreachable 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "382810877fe448991dfc7f0dd6e3ae5d58088fd0ea5e35189655f84e6814fa56"
 "checksum void 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "6a02e4885ed3bc0f2de90ea6dd45ebcbb66dacffe03547fadbb0eeae2770887d"
diff --git a/src/eval.rs b/src/eval.rs
index d9a4c84410..8b6bd716cd 100644
--- a/src/eval.rs
+++ b/src/eval.rs
@@ -7,6 +7,7 @@ use expr::Operator::*;
 use std::rc::Rc;
 use im_rc::hashmap::HashMap;
 use self::Evaluated::*;
+use smallvec::SmallVec;
 
 pub fn eval(expr: Expr) -> Evaluated {
     scoped_eval(expr, &HashMap::new())
@@ -133,7 +134,7 @@ fn eval_apply(expr: Evaluated, args: Vec<Expr>, vars: &Scope) -> Evaluated {
 }
 
 #[inline(always)]
-fn eval_closure(args: Vec<Evaluated>, arg_patterns: Vec<Pattern>, vars: &Scope)
+fn eval_closure(args: Vec<Evaluated>, arg_patterns: SmallVec<[Pattern; 4]>, vars: &Scope)
     -> Result<Scope, expr::Problem>
 {
     if arg_patterns.len() == args.len() {
@@ -224,7 +225,7 @@ fn eval_operator(Evaluated(left_expr): &Evaluated, op: Operator, Evaluated(right
 }
 
 #[inline(always)]
-fn eval_match (condition: Evaluated, branches: Vec<(Pattern, Box<Expr>)>, vars: &Scope) -> Evaluated {
+fn eval_match (condition: Evaluated, branches: SmallVec<[(Pattern, Box<Expr>); 4]>, vars: &Scope) -> Evaluated {
     let Evaluated(ref evaluated_expr) = condition;
 
     for (pattern, definition) in branches {
diff --git a/src/expr.rs b/src/expr.rs
index dc57c77761..113c182fd3 100644
--- a/src/expr.rs
+++ b/src/expr.rs
@@ -1,5 +1,6 @@
 use std::fmt;
 use self::Expr::*;
+use smallvec::SmallVec;
 
 #[derive(Clone, Debug, PartialEq)]
 pub enum Expr {
@@ -17,14 +18,14 @@ pub enum Expr {
     Func(String, Vec<Expr>),
     Apply(Box<Expr>, Vec<Expr>),
     Operator(Box<Expr>, Operator, Box<Expr>),
-    Closure(Vec<Pattern>, Box<Expr>),
+    Closure(SmallVec<[Pattern; 4]>, Box<Expr>),
 
     // Sum Types
     ApplyVariant(String, Option<Vec<Expr>>),
 
     // Conditionals
     If(Box<Expr>, Box<Expr>, Box<Expr>),
-    Match(Box<Expr>, Vec<(Pattern, Box<Expr>)>),
+    Match(Box<Expr>, SmallVec<[(Pattern, Box<Expr>); 4]>),
 
     // Error
     Error(Problem),
diff --git a/src/lib.rs b/src/lib.rs
index 6ef7923b81..97fbe0d44f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -12,4 +12,5 @@ extern crate dogged;
 
 extern crate im_rc;
 
+extern crate smallvec;
 #[macro_use] extern crate combine;
diff --git a/src/parse.rs b/src/parse.rs
index 2b976d5bcf..8b53fb3d7d 100644
--- a/src/parse.rs
+++ b/src/parse.rs
@@ -3,6 +3,7 @@ use expr::{Expr, Pattern};
 
 use std::char;
 use parse_state::{IndentablePosition};
+use smallvec::SmallVec;
 
 use combine::parser::char::{char, string, spaces, digit, hex_digit, HexDigit, alpha_num};
 use combine::parser::repeat::{many, count_min_max, sep_by1, skip_many, skip_many1};
@@ -206,7 +207,7 @@ where I: Stream<Item = char, Position = IndentablePosition>,
     string("match").skip(indented_whitespaces1(min_indent))
         .with(expr_body(min_indent)).skip(indented_whitespaces1(min_indent))
         .and(
-            many::<Vec<_>, _>(
+            many::<SmallVec<_>, _>(
                 string("when").skip(indented_whitespaces1(min_indent))
                     .with(pattern(min_indent)).skip(indented_whitespaces1(min_indent))
                     .skip(string("then")).skip(indented_whitespaces1(min_indent))
diff --git a/tests/test_parse.rs b/tests/test_parse.rs
index ba39b24e5a..9c90d8418b 100644
--- a/tests/test_parse.rs
+++ b/tests/test_parse.rs
@@ -1,4 +1,5 @@
 #[macro_use] extern crate pretty_assertions;
+#[macro_use] extern crate smallvec;
 extern crate combine;
 
 extern crate roc;
@@ -234,7 +235,7 @@ mod parse_tests {
     #[test]
     fn single_operator_with_var() {
         assert_eq!(
-            // It's important that this isn't mistaken for 
+            // It's important that this isn't mistaken for
             // a declaration like (x = 1)
             parse_standalone("x == 1"),
             Ok((Operator(