diff --git a/lightning-invoice/src/de.rs b/lightning-invoice/src/de.rs
index 7c425441f4e..da43edc5b6b 100644
--- a/lightning-invoice/src/de.rs
+++ b/lightning-invoice/src/de.rs
@@ -1,3 +1,4 @@
+use alloc::string;
 #[cfg(feature = "std")]
 use std::error;
 #[cfg(not(feature = "std"))]
@@ -5,7 +6,6 @@ use core::convert::TryFrom;
 use core::fmt;
 use core::fmt::{Display, Formatter};
 use core::num::ParseIntError;
-use core::str;
 use core::str::FromStr;
 
 use bech32::primitives::decode::{CheckedHrpstring, CheckedHrpstringError};
@@ -613,7 +613,7 @@ impl FromBase32 for Description {
 
 	fn from_base32(field_data: &[Fe32]) -> Result<Description, Bolt11ParseError> {
 		let bytes = Vec::<u8>::from_base32(field_data)?;
-		let description = String::from(str::from_utf8(&bytes)?);
+		let description = String::from_utf8(bytes)?;
 		Ok(Description::new(description).expect(
 			"Max len is 639=floor(1023*5/8) since the len field is only 10bits long"
 		))
@@ -712,7 +712,7 @@ impl FromBase32 for PrivateRoute {
 			return Err(Bolt11ParseError::UnexpectedEndOfTaggedFields);
 		}
 
-		let mut route_hops = Vec::<RouteHintHop>::new();
+		let mut route_hops = Vec::with_capacity(bytes.len() / 51);
 
 		let mut bytes = bytes.as_slice();
 		while !bytes.is_empty() {
@@ -824,7 +824,7 @@ macro_rules! from_error {
 
 from_error!(Bolt11ParseError::MalformedSignature, bitcoin::secp256k1::Error);
 from_error!(Bolt11ParseError::ParseAmountError, ParseIntError);
-from_error!(Bolt11ParseError::DescriptionDecodeError, str::Utf8Error);
+from_error!(Bolt11ParseError::DescriptionDecodeError, string::FromUtf8Error);
 
 impl From<CheckedHrpstringError> for Bolt11ParseError {
 	fn from(e: CheckedHrpstringError) -> Self {
diff --git a/lightning-invoice/src/lib.rs b/lightning-invoice/src/lib.rs
index 36370896052..8baedbe26cd 100644
--- a/lightning-invoice/src/lib.rs
+++ b/lightning-invoice/src/lib.rs
@@ -51,7 +51,7 @@ use core::num::ParseIntError;
 use core::ops::Deref;
 use core::slice::Iter;
 use core::time::Duration;
-use core::str;
+use alloc::string;
 
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Deserializer,Serialize, Serializer, de::Error};
@@ -98,7 +98,7 @@ pub enum Bolt11ParseError {
 	MalformedHRP,
 	TooShortDataPart,
 	UnexpectedEndOfTaggedFields,
-	DescriptionDecodeError(str::Utf8Error),
+	DescriptionDecodeError(string::FromUtf8Error),
 	PaddingError,
 	IntegerOverflowError,
 	InvalidSegWitProgramLength,
@@ -313,6 +313,7 @@ impl RawHrp {
 	pub fn to_hrp(&self) -> bech32::Hrp {
 		let hrp_str = self.to_string();
 		let s = core::str::from_utf8(&hrp_str.as_bytes()).expect("HRP bytes should be ASCII");
+		debug_assert!(bech32::Hrp::parse(s).is_ok(), "We should always build BIP 173-valid HRPs");
 		bech32::Hrp::parse_unchecked(s)
 	}
 }
diff --git a/lightning-invoice/src/ser.rs b/lightning-invoice/src/ser.rs
index 4000241f557..66571ee35f9 100644
--- a/lightning-invoice/src/ser.rs
+++ b/lightning-invoice/src/ser.rs
@@ -29,7 +29,7 @@ pub(crate) trait Base32Len: Base32Iterable {
 
 impl<const N: usize> Base32Iterable for [u8; N] {
 	fn fe_iter<'s>(&'s self) -> Box<dyn Iterator<Item = Fe32> + 's> {
-		Box::new((*self).into_iter().bytes_to_fes())
+		self[..].fe_iter()
 	}
 }
 
@@ -218,19 +218,20 @@ impl Display for SiPrefix {
 }
 
 /// Encode an integer to base32, big endian, without leading zeros
-fn encode_int_be_base32(int: u64) -> Vec<Fe32> {
+fn encode_int_be_base32(int: u64) -> impl ExactSizeIterator<Item=Fe32> {
 	let base = 32u64;
 
 	// (64 + 4) / 5 == 13
-	let mut out_vec = Vec::<Fe32>::with_capacity(13);
+	let mut out = [Fe32::Q; 13];
+	let mut out_pos = 0;
 	let mut rem_int = int;
 	while rem_int != 0 {
-		out_vec.push(Fe32::try_from((rem_int % base) as u8).expect("always <32"));
+		out[out_pos] = Fe32::try_from((rem_int % base) as u8).expect("always <32");
+		out_pos += 1;
 		rem_int /= base;
 	}
 
-	out_vec.reverse();
-	out_vec
+	out.into_iter().take(out_pos).rev()
 }
 
 /// The length of the output of `encode_int_be_base32`.
@@ -252,7 +253,7 @@ impl Base32Iterable for PositiveTimestamp {
 		let fes = encode_int_be_base32(self.as_unix_timestamp());
 		debug_assert!(fes.len() <= 7, "Invalid timestamp length");
 		let to_pad = 7 - fes.len();
-		Box::new(core::iter::repeat(Fe32::Q).take(to_pad).chain(fes.into_iter()))
+		Box::new(core::iter::repeat(Fe32::Q).take(to_pad).chain(fes))
 	}
 }
 
@@ -305,7 +306,7 @@ impl Base32Len for PayeePubKey {
 
 impl Base32Iterable for ExpiryTime {
 	fn fe_iter<'s>(&'s self) -> Box<dyn Iterator<Item = Fe32> + 's> {
-		Box::new(encode_int_be_base32(self.as_seconds()).into_iter())
+		Box::new(encode_int_be_base32(self.as_seconds()))
 	}
 }
 
@@ -317,7 +318,7 @@ impl Base32Len for ExpiryTime {
 
 impl Base32Iterable for MinFinalCltvExpiryDelta {
 	fn fe_iter<'s>(&'s self) -> Box<dyn Iterator<Item = Fe32> + 's> {
-		Box::new(encode_int_be_base32(self.0).into_iter())
+		Box::new(encode_int_be_base32(self.0))
 	}
 }
 
@@ -504,6 +505,6 @@ mod test {
 			.map(|v| Fe32::try_from(v).expect("<= 31"))
 			.collect::<Vec<Fe32>>();
 
-		assert_eq!(expected_out, encode_int_be_base32(input));
+		assert_eq!(expected_out, encode_int_be_base32(input).collect::<Vec<Fe32>>());
 	}
 }
diff --git a/lightning/src/offers/parse.rs b/lightning/src/offers/parse.rs
index a46e90de6be..7c9d80387de 100644
--- a/lightning/src/offers/parse.rs
+++ b/lightning/src/offers/parse.rs
@@ -58,7 +58,7 @@ mod sealed {
 
 			let parsed = CheckedHrpstring::new::<NoChecksum>(encoded.as_ref())?;
 			let hrp = parsed.hrp();
-			if hrp.to_string() != Self::BECH32_HRP {
+			if hrp.as_str() != Self::BECH32_HRP {
 				return Err(Bolt12ParseError::InvalidBech32Hrp);
 			}