diff --git a/src/librustc/diagnostics.rs b/src/librustc/diagnostics.rs
index de68cc707ad7a..142f8f5c719c2 100644
--- a/src/librustc/diagnostics.rs
+++ b/src/librustc/diagnostics.rs
@@ -1431,6 +1431,23 @@ fn make_child<'elve>(x: &mut &'elve isize, y: &mut &'elve isize) {
 ```
 "##,
 
+E0317: r##"
+This error occurs when an `if` expression without an `else` block is used in a
+context where a type other than `()` is expected, for example a `let`
+expression:
+
+```compile_fail,E0317
+fn main() {
+    let x = 5;
+    let a = if x == 5 { 1 };
+}
+```
+
+An `if` expression without an `else` block has the type `()`, so this is a type
+error. To resolve it, add an `else` block having the same type as the `if`
+block.
+"##,
+
 E0398: r##"
 In Rust 1.3, the default object lifetime bounds are expected to change, as
 described in RFC #1156 [1]. You are getting a warning because the compiler
diff --git a/src/librustc/infer/error_reporting.rs b/src/librustc/infer/error_reporting.rs
index 3f216d6916851..373ea4aac57b0 100644
--- a/src/librustc/infer/error_reporting.rs
+++ b/src/librustc/infer/error_reporting.rs
@@ -577,11 +577,16 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                                          terr: &TypeError<'tcx>)
                                          -> DiagnosticBuilder<'tcx>
     {
-        // FIXME: do we want to use a different error code for each origin?
-        let mut diag = struct_span_err!(
-            self.tcx.sess, trace.origin.span(), E0308,
-            "{}", trace.origin.as_failure_str()
-        );
+        let span = trace.origin.span();
+        let failure_str = trace.origin.as_failure_str();
+        let mut diag = match trace.origin {
+            TypeOrigin::IfExpressionWithNoElse(_) => {
+                struct_span_err!(self.tcx.sess, span, E0317, "{}", failure_str)
+            },
+            _ => {
+                struct_span_err!(self.tcx.sess, span, E0308, "{}", failure_str)
+            },
+        };
         self.note_type_err(&mut diag, trace.origin, None, Some(trace.values), terr);
         diag
     }
diff --git a/src/test/compile-fail/if-without-else-result.rs b/src/test/compile-fail/if-without-else-result.rs
index e8aa1f70ea1dc..95bcce5a8474a 100644
--- a/src/test/compile-fail/if-without-else-result.rs
+++ b/src/test/compile-fail/if-without-else-result.rs
@@ -10,7 +10,7 @@
 
 fn main() {
     let a = if true { true };
-    //~^ ERROR if may be missing an else clause
+    //~^ ERROR if may be missing an else clause [E0317]
     //~| expected type `()`
     //~| found type `bool`
     //~| expected (), found bool