diff --git a/artiq/compiler/transforms/inferencer.py b/artiq/compiler/transforms/inferencer.py
index 2e0bd629b..2d96d1372 100644
--- a/artiq/compiler/transforms/inferencer.py
+++ b/artiq/compiler/transforms/inferencer.py
@@ -708,6 +708,7 @@ class Inferencer(algorithm.Visitor):
         elif types.is_builtin(typ, "round"):
             valid_forms = lambda: [
                 valid_form("round(x:float) -> int(width='a)"),
+                valid_form("round(x:float, width='b:<int literal>) -> int(width='b)")
             ]
 
             self._unify(node.type, builtins.TInt(),
@@ -718,6 +719,19 @@ class Inferencer(algorithm.Visitor):
 
                 self._unify(arg.type, builtins.TFloat(),
                             arg.loc, None)
+            elif len(node.args) == 1 and len(node.keywords) == 1 and \
+                    builtins.is_numeric(node.args[0].type) and \
+                    node.keywords[0].arg == 'width':
+                width = node.keywords[0].value
+                if not (isinstance(width, asttyped.NumT) and isinstance(width.n, int)):
+                    diag = diagnostic.Diagnostic("error",
+                        "the width argument of round() must be an integer literal", {},
+                        node.keywords[0].loc)
+                    self.engine.process(diag)
+                    return
+
+                self._unify(node.type, builtins.TInt(types.TValue(width.n)),
+                            node.loc, None)
             else:
                 diagnose(valid_forms())
         elif types.is_builtin(typ, "print"):
diff --git a/lit-test/test/inferencer/builtin_calls.py b/lit-test/test/inferencer/builtin_calls.py
index 61a97fb4a..1b3157e2e 100644
--- a/lit-test/test/inferencer/builtin_calls.py
+++ b/lit-test/test/inferencer/builtin_calls.py
@@ -30,3 +30,6 @@ len([])
 
 # CHECK-L: round:<function round>(1.0:float):int(width='h)
 round(1.0)
+
+# CHECK-L: round:<function round>(1.0:float, width=64:int(width='i)):int(width=64)
+round(1.0, width=64)