diff --git a/components/style/properties/gecko.mako.rs b/components/style/properties/gecko.mako.rs
index 1c26c4a8f5a..d1f06601bb5 100644
--- a/components/style/properties/gecko.mako.rs
+++ b/components/style/properties/gecko.mako.rs
@@ -1324,7 +1324,7 @@ fn static_assert() {
 <%def name="impl_animation_time_value(ident, gecko_ffi_name)">
     #[allow(non_snake_case)]
     pub fn set_animation_${ident}(&mut self, v: longhands::animation_${ident}::computed_value::T) {
-        assert!(v.0.len() > 0);
+        debug_assert!(!v.0.is_empty());
         unsafe { self.gecko.mAnimations.ensure_len(v.0.len()) };
 
         self.gecko.mAnimation${gecko_ffi_name}Count = v.0.len() as u32;
@@ -1348,7 +1348,7 @@ fn static_assert() {
         use properties::longhands::animation_${ident}::single_value::computed_value::T as Keyword;
         use gecko_bindings::structs;
 
-        assert!(v.0.len() > 0);
+        debug_assert!(!v.0.is_empty());
         unsafe { self.gecko.mAnimations.ensure_len(v.0.len()) };
 
         self.gecko.mAnimation${gecko_ffi_name}Count = v.0.len() as u32;
@@ -1773,7 +1773,7 @@ fn static_assert() {
         use std::f32;
         use properties::longhands::animation_iteration_count::single_value::SpecifiedValue as AnimationIterationCount;
 
-        assert!(v.0.len() > 0);
+        debug_assert!(!v.0.is_empty());
         unsafe { self.gecko.mAnimations.ensure_len(v.0.len()) };
 
         self.gecko.mAnimationIterationCountCount = v.0.len() as u32;
@@ -1799,7 +1799,7 @@ fn static_assert() {
     ${impl_copy_animation_value('iteration_count', 'IterationCount')}
 
     pub fn set_animation_timing_function(&mut self, v: longhands::animation_timing_function::computed_value::T) {
-        assert!(v.0.len() > 0);
+        debug_assert!(!v.0.is_empty());
         unsafe { self.gecko.mAnimations.ensure_len(v.0.len()) };
 
         self.gecko.mAnimationTimingFunctionCount = v.0.len() as u32;