diff --git a/src/config.rs b/src/config.rs
index 5b6a5e05cf5..48b7a06e538 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -316,6 +316,7 @@ create_config! {
     where_layout: ListTactic, ListTactic::Vertical, "Element layout inside a where clause";
     where_pred_indent: BlockIndentStyle, BlockIndentStyle::Visual,
         "Indentation style of a where predicate";
+    where_trailing_comma: bool, false, "Put a trailing comma on where clauses";
     generics_indent: BlockIndentStyle, BlockIndentStyle::Visual, "Indentation of generics";
     struct_trailing_comma: SeparatorTactic, SeparatorTactic::Vertical,
         "If there is a trailing comma on structs";
diff --git a/src/items.rs b/src/items.rs
index 1e1b6ca8076..2ff52148f6a 100644
--- a/src/items.rs
+++ b/src/items.rs
@@ -491,6 +491,7 @@ pub fn format_impl(context: &RewriteContext, item: &ast::Item, offset: Indent) -
                                                              where_budget,
                                                              context.config.where_density,
                                                              "{",
+                                                             true,
                                                              None));
 
         if try_opt!(is_impl_single_line(context, &items, &result, &where_clause_str, &item)) {
@@ -737,6 +738,7 @@ fn format_tuple_struct(context: &RewriteContext,
                                           where_budget,
                                           Density::Compressed,
                                           ";",
+                                          false,
                                           None))
         }
         None => "".to_owned(),
@@ -818,6 +820,7 @@ pub fn rewrite_type_alias(context: &RewriteContext,
                                                          where_budget,
                                                          context.config.where_density,
                                                          "=",
+                                                         false,
                                                          Some(span.hi)));
     result.push_str(&where_clause_str);
     result.push_str(" = ");
@@ -1248,6 +1251,7 @@ fn rewrite_fn_base(context: &RewriteContext,
                                                          where_budget,
                                                          where_density,
                                                          "{",
+                                                         has_body,
                                                          Some(span.hi)));
 
     if last_line_width(&result) + where_clause_str.len() > context.config.max_width &&
@@ -1487,6 +1491,7 @@ fn rewrite_where_clause(context: &RewriteContext,
                         width: usize,
                         density: Density,
                         terminator: &str,
+                        allow_trailing_comma: bool,
                         span_end: Option<BytePos>)
                         -> Option<String> {
     if where_clause.predicates.is_empty() {
@@ -1526,11 +1531,12 @@ fn rewrite_where_clause(context: &RewriteContext,
     // FIXME: we don't need to collect here if the where_layout isn't
     // HorizontalVertical.
     let tactic = definitive_tactic(&item_vec, context.config.where_layout, budget);
+    let use_trailing_comma = allow_trailing_comma && context.config.where_trailing_comma;
 
     let fmt = ListFormatting {
         tactic: tactic,
         separator: ",",
-        trailing_separator: SeparatorTactic::Never,
+        trailing_separator: SeparatorTactic::from_bool(use_trailing_comma),
         indent: offset,
         width: budget,
         ends_with_newline: true,
@@ -1592,6 +1598,7 @@ fn format_generics(context: &RewriteContext,
                                                              budget,
                                                              Density::Tall,
                                                              terminator,
+                                                             true,
                                                              Some(span.hi)));
         result.push_str(&where_clause_str);
         if !force_same_line_brace &&
diff --git a/tests/config/small_tabs.toml b/tests/config/small_tabs.toml
index 1681aff77b4..cb4d5da5274 100644
--- a/tests/config/small_tabs.toml
+++ b/tests/config/small_tabs.toml
@@ -12,6 +12,7 @@ where_density = "Tall"
 where_indent = "Tabbed"
 where_layout = "Vertical"
 where_pred_indent = "Visual"
+where_trailing_comma = false
 generics_indent = "Visual"
 struct_trailing_comma = "Vertical"
 struct_lit_trailing_comma = "Vertical"
diff --git a/tests/source/where-trailing-comma.rs b/tests/source/where-trailing-comma.rs
new file mode 100644
index 00000000000..8f951d199e4
--- /dev/null
+++ b/tests/source/where-trailing-comma.rs
@@ -0,0 +1,37 @@
+// rustfmt-where_trailing_comma: true
+
+fn f<S, T>(x: T, y: S) -> T where T: P, S: Q
+{
+    x
+}
+
+impl Trait for T where T: P
+{
+    fn f(x: T) -> T where T: Q + R
+    {
+        x
+    }
+}
+
+struct Pair<S, T> where T: P, S: P + Q {
+    a: T,
+    b: S
+}
+
+struct TupPair<S, T> (S, T) where T: P, S: P + Q;
+
+enum E<S, T> where S: P, T: P { 
+    A {a: T},
+}
+
+type Double<T> where T: P, T: Q = Pair<T, T>;
+
+extern "C" {
+    fn f<S, T>(x: T, y: S) -> T where T: P, S: Q;
+}
+
+// Note: trait declarations are not fully formatted (issue #78)
+trait Q<S, T> where T: P, S: R
+{
+    fn f<U, V>(self, x: T, y: S, z: U) -> Self where U: P, V: P;
+}
diff --git a/tests/target/where-trailing-comma.rs b/tests/target/where-trailing-comma.rs
new file mode 100644
index 00000000000..bd7108f992a
--- /dev/null
+++ b/tests/target/where-trailing-comma.rs
@@ -0,0 +1,57 @@
+// rustfmt-where_trailing_comma: true
+
+fn f<S, T>(x: T, y: S) -> T
+    where T: P,
+          S: Q,
+{
+    x
+}
+
+impl Trait for T
+    where T: P,
+{
+    fn f(x: T) -> T
+        where T: Q + R,
+    {
+        x
+    }
+}
+
+struct Pair<S, T>
+    where T: P,
+          S: P + Q,
+{
+    a: T,
+    b: S,
+}
+
+struct TupPair<S, T>(S, T)
+    where T: P,
+          S: P + Q;
+
+enum E<S, T>
+    where S: P,
+          T: P,
+{
+    A {
+        a: T,
+    },
+}
+
+type Double<T>
+    where T: P,
+          T: Q = Pair<T, T>;
+
+extern "C" {
+    fn f<S, T>(x: T, y: S) -> T
+        where T: P,
+              S: Q;
+}
+
+// Note: trait declarations are not fully formatted (issue #78)
+trait Q<S, T> where T: P, S: R
+{
+    fn f<U, V>(self, x: T, y: S, z: U) -> Self
+        where U: P,
+              V: P;
+}