diff --git a/components/ProgressView/src/MDCProgressView.h b/components/ProgressView/src/MDCProgressView.h
index ea943c246ac..ef54877c7a3 100644
--- a/components/ProgressView/src/MDCProgressView.h
+++ b/components/ProgressView/src/MDCProgressView.h
@@ -56,7 +56,7 @@ IB_DESIGNABLE
 
  The default is nil.
 */
-@property(nonatomic, copy, nullable) NSArray *progressTintColors;
+@property(nonatomic, copy, nullable) NSArray<UIColor *> *progressTintColors;
 
 /**
  The color shown for the portion of the progress view that is not filled.
diff --git a/components/ProgressView/src/MDCProgressView.m b/components/ProgressView/src/MDCProgressView.m
index 0beb13b1171..1da69dd46e7 100644
--- a/components/ProgressView/src/MDCProgressView.m
+++ b/components/ProgressView/src/MDCProgressView.m
@@ -140,7 +140,7 @@ - (void)setProgressTintColor:(UIColor *)progressTintColor {
   }
 }
 
-- (void)setProgressTintColors:(NSArray *)progressTintColors {
+- (void)setProgressTintColors:(NSArray<UIColor *> *)progressTintColors {
   _progressTintColors = [progressTintColors copy];
   _progressTintColor = nil;
   self.progressView.colors = _progressTintColors;