diff --git a/token/program-2022-test/tests/scaled_ui_amount.rs b/token/program-2022-test/tests/scaled_ui_amount.rs
index 78fd4433735..062e6fafad8 100644
--- a/token/program-2022-test/tests/scaled_ui_amount.rs
+++ b/token/program-2022-test/tests/scaled_ui_amount.rs
@@ -84,6 +84,27 @@ async fn fail_initialize_with_interest_bearing() {
     );
 }
 
+#[tokio::test]
+async fn fail_initialize_with_bad_multiplier() {
+    let mut context = TestContext::new().await;
+    let err = context
+        .init_token_with_mint(vec![ExtensionInitializationParams::ScaledUiAmountConfig {
+            authority: None,
+            multiplier: 0.0,
+        }])
+        .await
+        .unwrap_err();
+    assert_eq!(
+        err,
+        TokenClientError::Client(Box::new(TransportError::TransactionError(
+            TransactionError::InstructionError(
+                1,
+                InstructionError::Custom(TokenError::InvalidScale as u32)
+            )
+        )))
+    );
+}
+
 #[tokio::test]
 async fn update_multiplier() {
     let authority = Keypair::new();
@@ -115,6 +136,21 @@ async fn update_multiplier() {
     assert_eq!(f64::from(extension.new_multiplier), new_multiplier);
     assert_eq!(i64::from(extension.new_multiplier_effective_timestamp), 0);
 
+    // fail, bad number
+    let err = token
+        .update_multiplier(&authority.pubkey(), f64::INFINITY, 0, &[&authority])
+        .await
+        .unwrap_err();
+    assert_eq!(
+        err,
+        TokenClientError::Client(Box::new(TransportError::TransactionError(
+            TransactionError::InstructionError(
+                0,
+                InstructionError::Custom(TokenError::InvalidScale as u32)
+            )
+        )))
+    );
+
     // correct in the future
     let newest_multiplier = 100.0;
     token
diff --git a/token/program-2022/src/extension/scaled_ui_amount/instruction.rs b/token/program-2022/src/extension/scaled_ui_amount/instruction.rs
index 9dc092714f9..cb939f6a675 100644
--- a/token/program-2022/src/extension/scaled_ui_amount/instruction.rs
+++ b/token/program-2022/src/extension/scaled_ui_amount/instruction.rs
@@ -28,7 +28,8 @@ pub enum ScaledUiAmountMintInstruction {
     /// Fails if the mint has already been initialized, so must be called before
     /// `InitializeMint`.
     ///
-    /// Fails with any number less than 0.
+    /// Fails if the multiplier is less than or equal to 0 or if it's
+    /// [subnormal](https://en.wikipedia.org/wiki/Subnormal_number).
     ///
     /// The mint must have exactly enough space allocated for the base mint (82
     /// bytes), plus 83 bytes of padding, 1 byte reserved for the account type,
@@ -44,6 +45,9 @@ pub enum ScaledUiAmountMintInstruction {
     /// Update the multiplier. Only supported for mints that include the
     /// `ScaledUiAmount` extension.
     ///
+    /// Fails if the multiplier is less than or equal to 0 or if it's
+    /// [subnormal](https://en.wikipedia.org/wiki/Subnormal_number).
+    ///
     /// The authority provides a new multiplier and a unix timestamp on which
     /// it should take effect. If the timestamp is before the current time,
     /// immediately sets the multiplier.