diff --git a/documentation/intermediate-dsl.md b/documentation/intermediate-dsl.md
index 40aa783b..c37f05a3 100644
--- a/documentation/intermediate-dsl.md
+++ b/documentation/intermediate-dsl.md
@@ -945,7 +945,7 @@ MOS {
 ### MOS declaration syntax
 The syntax for MOS declarations withing the curly brackets after `MOS` is as follows:
 
-Below `n` is an integer, `x` and `y` are integers in the range from 1 to 9, and `expr` is any SonicWeave expression that evaluates to a radical interval. Syntax followed by a question mark is optional.
+Below `n` is an integer, `x` and `y` are integers in the range from 1 to 9, and `expr` is any SonicWeave expression that evaluates to an interval. Syntax followed by a question mark is optional.
 | Name                 | Pattern                              |
 | -------------------- | ------------------------------------ |
 | Counts with UDP      | `nL ns up\|down(period)? <equave>?`  |
diff --git a/src/diamond-mos.ts b/src/diamond-mos.ts
index 6b5fda9b..2bf98418 100644
--- a/src/diamond-mos.ts
+++ b/src/diamond-mos.ts
@@ -11,6 +11,8 @@ import {
 } from './pythagorean';
 import {ZERO} from './utils';
 
+type Monzo = TimeMonzo | TimeReal;
+
 /**
  * Base degree for a mosstep in a 0-indexed array.
  */
@@ -18,7 +20,7 @@ export type MosDegree = {
   /**
    * The perfect or neutral central interval.
    */
-  center: TimeMonzo;
+  center: Monzo;
   /**
    * Flag to indicate if the degree has minor and major variants.
    */
@@ -26,7 +28,7 @@ export type MosDegree = {
   /**
    * The lopsided neutral variant of a bright or dark generator.
    */
-  mid?: TimeMonzo;
+  mid?: Monzo;
 };
 
 /**
@@ -37,23 +39,23 @@ export type MosConfig = {
   /**
    * Interval of equivalence. The distance between J4 and J5.
    */
-  equave: TimeMonzo;
+  equave: Monzo;
   /**
    * Period of repetition.
    */
-  period: TimeMonzo;
+  period: Monzo;
   /**
    * Current value of the '&' accidental.
    */
-  am: TimeMonzo;
+  am: Monzo;
   /**
    * Current value of the 'e' accidental.
    */
-  semiam: TimeMonzo;
+  semiam: Monzo;
   /**
    * Relative scale from J onwards. Echelon depends on J. Use equave to reach higher octave numbers.
    */
-  scale: Map<string, TimeMonzo>;
+  scale: Map<string, Monzo>;
   /**
    * Intervals for relative notation. Use period to reach larger intervals.
    */
@@ -65,11 +67,11 @@ export type MosConfig = {
   /**
    * Value of the large step.
    */
-  large: TimeMonzo;
+  large: Monzo;
   /**
    * Value of the small step.
    */
-  small: TimeMonzo;
+  small: Monzo;
 };
 
 /**
@@ -125,7 +127,7 @@ export function scaleMonzos(config: MosConfig) {
         : a[0].localeCompare(b[0])
   );
   const monzos = entries.map(entry => entry[1]);
-  monzos.push(monzos.shift()!.mul(config.equave) as TimeMonzo);
+  monzos.push(monzos.shift()!.mul(config.equave));
   return monzos;
 }
 
@@ -135,12 +137,12 @@ export function scaleMonzos(config: MosConfig) {
  * @param config Result of a MOS declaration.
  * @returns A relative time monzo.
  */
-export function mosMonzo(node: MosStep, config: MosConfig): TimeMonzo {
+export function mosMonzo(node: MosStep, config: MosConfig): Monzo {
   const baseDegree = mmod(Math.abs(node.degree), config.degrees.length);
   const periods = (node.degree - baseDegree) / config.degrees.length;
   const mosDegree = config.degrees[baseDegree];
   const quality = node.quality.quality;
-  let inflection = new TimeMonzo(ZERO, []);
+  let inflection: Monzo = new TimeMonzo(ZERO, []);
   if (
     quality === 'a' ||
     quality === 'Â' ||
@@ -158,17 +160,14 @@ export function mosMonzo(node: MosStep, config: MosConfig): TimeMonzo {
   if (node.quality.fraction !== '') {
     const fraction = VULGAR_FRACTIONS.get(node.quality.fraction)!;
     const fractionalInflection = inflection.pow(fraction);
-    if (fractionalInflection instanceof TimeReal) {
-      throw new Error('Failed to fractionally inflect mosstep.');
-    }
     inflection = fractionalInflection;
   }
 
   for (const augmentation of node.augmentations ?? []) {
     if (augmentation === 'd' || augmentation === 'dim') {
-      inflection = inflection.div(config.am) as TimeMonzo;
+      inflection = inflection.div(config.am);
     } else {
-      inflection = inflection.mul(config.am) as TimeMonzo;
+      inflection = inflection.mul(config.am);
     }
   }
 
@@ -180,9 +179,9 @@ export function mosMonzo(node: MosStep, config: MosConfig): TimeMonzo {
       quality === 'aug' ||
       quality === 'Aug'
     ) {
-      inflection = inflection.mul(config.semiam) as TimeMonzo;
+      inflection = inflection.mul(config.semiam);
     } else if (quality === 'd' || quality === 'dim') {
-      inflection = inflection.div(config.semiam) as TimeMonzo;
+      inflection = inflection.div(config.semiam);
     }
     if (quality === 'P') {
       throw new Error(
@@ -199,9 +198,7 @@ export function mosMonzo(node: MosStep, config: MosConfig): TimeMonzo {
       `The mosstep ${baseDegree} does not have minor or major variants.`
     );
   }
-  return mosDegree.center
-    .mul(inflection)
-    .mul(config.period.pow(periods)) as TimeMonzo;
+  return mosDegree.center.mul(inflection).mul(config.period.pow(periods));
 }
 
 function mosInflection(
@@ -234,7 +231,7 @@ function mosInflection(
 export function absoluteMosMonzo(
   node: AbsoluteMosPitch,
   config: MosConfig
-): TimeMonzo {
+): Monzo {
   if (!config.scale.has(node.nominal)) {
     throw new Error(`Nominal ${node.nominal} is unassigned.`);
   }
@@ -244,10 +241,7 @@ export function absoluteMosMonzo(
 
     const fraction = VULGAR_FRACTIONS.get(accidental.fraction)!;
     const fractionalInflection = inflection.pow(fraction);
-    if (fractionalInflection instanceof TimeReal) {
-      throw new Error('Failed to fracture mos accidental.');
-    }
-    result = result.mul(fractionalInflection) as TimeMonzo;
+    result = result.mul(fractionalInflection);
   }
-  return result.mul(config.equave.pow(node.octave - 4)) as TimeMonzo;
+  return result.mul(config.equave.pow(node.octave - 4));
 }
diff --git a/src/fjs.ts b/src/fjs.ts
index 3fed2da0..d0c7552f 100644
--- a/src/fjs.ts
+++ b/src/fjs.ts
@@ -325,7 +325,7 @@ export function getInflection(
 }
 
 export function inflect(
-  pythagorean: TimeMonzo,
+  pythagorean: TimeMonzo | TimeReal,
   superscripts: FJSInflection[],
   subscripts: FJSInflection[]
 ) {
diff --git a/src/parser/__tests__/source.spec.ts b/src/parser/__tests__/source.spec.ts
index e9fe4563..12e8fb7f 100644
--- a/src/parser/__tests__/source.spec.ts
+++ b/src/parser/__tests__/source.spec.ts
@@ -1622,6 +1622,26 @@ describe('SonicWeave parser', () => {
     ]);
   });
 
+  it('supports irrational hardness in MOS declaration', () => {
+    const scale = expand(`
+      MOS {
+        5L 2s
+        hardness = PI
+      }
+      automos()
+      MOS niente
+    `);
+    expect(scale).toEqual([
+      '212.8935511816436r¢',
+      '425.7871023632872r¢',
+      '638.6806535449307r¢',
+      '706.446775590823r¢',
+      '919.3403267724666r¢',
+      '1132.23387795411r¢',
+      '1200.0000000000025r¢',
+    ]);
+  });
+
   it('supports radicals in SOV', () => {
     const scale = expand(`
       9/8
diff --git a/src/parser/mos.ts b/src/parser/mos.ts
index add6f340..844f7801 100644
--- a/src/parser/mos.ts
+++ b/src/parser/mos.ts
@@ -22,10 +22,12 @@ import {Interval} from '../interval';
 import {MosConfig, MosDegree} from '../diamond-mos';
 import {ONE, TWO, ZERO} from '../utils';
 
+type Monzo = TimeMonzo | TimeReal;
+
 const TWO_MONZO = new TimeMonzo(ZERO, [ONE]);
 
-function realize(mosMonzo: MosMonzo, large: TimeMonzo, small: TimeMonzo) {
-  return large.pow(mosMonzo[0]).mul(small.pow(mosMonzo[1])) as TimeMonzo;
+function realize(mosMonzo: MosMonzo, large: Monzo, small: Monzo) {
+  return large.pow(mosMonzo[0]).mul(small.pow(mosMonzo[1]));
 }
 
 /**
@@ -33,10 +35,10 @@ function realize(mosMonzo: MosMonzo, large: TimeMonzo, small: TimeMonzo) {
  */
 export class Tardigrade {
   subVisitor: ExpressionVisitor;
-  equave?: TimeMonzo;
-  hardness?: TimeMonzo | TimeReal;
-  large?: TimeMonzo;
-  small?: TimeMonzo;
+  equave?: Monzo;
+  hardness?: Monzo;
+  large?: Monzo;
+  small?: Monzo;
   pattern?: string;
 
   constructor(subVisitor: ExpressionVisitor) {
@@ -56,8 +58,8 @@ export class Tardigrade {
     const N = new Fraction(this.pattern.length);
     const countL = new Fraction((this.pattern.match(/L/g) ?? []).length);
     const countS = N.sub(countL);
-    let small: TimeMonzo | TimeReal;
-    let large: TimeMonzo | TimeReal;
+    let small: Monzo;
+    let large: Monzo;
     if (this.equave) {
       if (this.hardness) {
         if (this.hardness.valueOf() === Infinity) {
@@ -78,14 +80,10 @@ export class Tardigrade {
         }
       } else if (this.large) {
         large = this.large;
-        small = this.equave
-          .div(large.pow(countL))
-          .pow(countS.inverse()) as TimeMonzo;
+        small = this.equave.div(large.pow(countL)).pow(countS.inverse());
       } else if (this.small) {
         small = this.small;
-        large = this.equave
-          .div(small.pow(countS))
-          .pow(countL.inverse()) as TimeMonzo;
+        large = this.equave.div(small.pow(countS)).pow(countL.inverse());
       } else {
         // Assume basic
         small = this.equave.pow(countL.mul(TWO).add(countS).inverse());
@@ -150,15 +148,10 @@ export class Tardigrade {
       throw new Error('Inconsistent MOS declaration.');
     }
 
-    if (large instanceof TimeReal || small instanceof TimeReal) {
-      throw new Error('MOS declaration must remain radical.');
-    }
-
     const am = large.div(small) as TimeMonzo;
     const semiam = am.sqrt() as TimeMonzo;
-    const r = (m: MosMonzo) =>
-      realize(m, large as TimeMonzo, small as TimeMonzo);
-    const scale = notation.scale as unknown as Map<string, TimeMonzo>;
+    const r = (m: MosMonzo) => realize(m, large, small);
+    const scale = notation.scale as unknown as Map<string, Monzo>;
     for (const [key, value] of notation.scale) {
       scale.set(key, r(value));
     }
@@ -263,9 +256,6 @@ export class Tardigrade {
     if (node.type === 'HardnessDeclaration' && value.valueOf() === Infinity) {
       return (this.hardness = value.value);
     }
-    if (!(value.value instanceof TimeMonzo)) {
-      throw new Error(`${node.type} must evaluate to a radical.`);
-    }
     switch (node.type) {
       case 'HardnessDeclaration':
         return (this.hardness = value.value);
diff --git a/src/stdlib/builtin.ts b/src/stdlib/builtin.ts
index d03cb996..74a4fb8f 100644
--- a/src/stdlib/builtin.ts
+++ b/src/stdlib/builtin.ts
@@ -1971,7 +1971,7 @@ function automos(this: ExpressionVisitor) {
   this.spendGas(this.rootContext.mosConfig.scale.size);
   const J4 = this.rootContext.C4;
   const monzos = scaleMonzos(this.rootContext.mosConfig).map(m => J4.mul(m));
-  return monzos.map(
+  const result = monzos.map(
     (m, i) =>
       new Interval(m, 'logarithmic', 0, {
         type: 'AbsoluteFJS',
@@ -1987,6 +1987,8 @@ function automos(this: ExpressionVisitor) {
         subscripts: [],
       })
   );
+  this.rootContext.fragiles.push(...result);
+  return result;
 }
 automos.__doc__ =
   'If the current scale is empty, generate absolute Diamond-mos notation based on the current config.';