diff --git a/src/client/components/mfm.ts b/src/client/components/mfm.ts
index 1590e29142..bca469a159 100644
--- a/src/client/components/mfm.ts
+++ b/src/client/components/mfm.ts
@@ -48,6 +48,11 @@ export default defineComponent({
 
 		const ast = (this.plain ? parsePlain : parse)(this.text);
 
+		const validTime = (t: string | null | undefined) => {
+			if (t == null) return null;
+			return t.match(/^[0-9.]+s$/) ? t : null;
+		};
+
 		const genEl = (ast: MfmForest) => concat(ast.map((token): VNode[] => {
 			switch (token.node.type) {
 				case 'text': {
@@ -86,17 +91,17 @@ export default defineComponent({
 							break;
 						}
 						case 'jelly': {
-							const speed = token.node.props.args.speed || '1s';
+							const speed = validTime(token.node.props.args.speed) || '1s';
 							style = (this.$store.state.animatedMfm ? `animation: mfm-rubberBand ${speed} linear infinite both;` : '');
 							break;
 						}
 						case 'twitch': {
-							const speed = token.node.props.args.speed || '0.5s';
+							const speed = validTime(token.node.props.args.speed) || '0.5s';
 							style = this.$store.state.animatedMfm ? `animation: mfm-twitch ${speed} ease infinite;` : '';
 							break;
 						}
 						case 'shake': {
-							const speed = token.node.props.args.speed || '0.5s';
+							const speed = validTime(token.node.props.args.speed) || '0.5s';
 							style = this.$store.state.animatedMfm ? `animation: mfm-shake ${speed} ease infinite;` : '';
 							break;
 						}
@@ -109,7 +114,7 @@ export default defineComponent({
 								token.node.props.args.x ? 'mfm-spinX' :
 								token.node.props.args.y ? 'mfm-spinY' :
 								'mfm-spin';
-							const speed = token.node.props.args.speed || '1.5s';
+							const speed = validTime(token.node.props.args.speed) || '1.5s';
 							style = this.$store.state.animatedMfm ? `animation: ${anime} ${speed} linear infinite; animation-direction: ${direction};` : '';
 							break;
 						}