diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a354eb72..a04c965e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -93,11 +93,7 @@ jobs:
     strategy:
       matrix:
         target: ["x86_64-unknown-linux-gnu", "thumbv6m-none-eabi"]
-        features:
-          [
-            "",
-            "derive",
-          ]
+        features: ["", "derive"]
         include:
           - target: "x86_64-unknown-linux-gnu"
             extra_features: "std,log"
@@ -138,4 +134,4 @@ jobs:
         uses: actions-rs/cargo@v1
         with:
           command: test
-          args: --workspace --features std,heapless
\ No newline at end of file
+          args: --workspace --features std,heapless,string_errors
diff --git a/atat/Cargo.toml b/atat/Cargo.toml
index 02a9ac81..99468ce1 100644
--- a/atat/Cargo.toml
+++ b/atat/Cargo.toml
@@ -53,3 +53,4 @@ custom-error-messages = []
 std = ["serde_at/std", "nom/std", "embassy-time/std", "embedded-io/std"]
 hex_str_arrays = []
 heapless = ["serde_at/heapless"]
+string_errors = []
diff --git a/atat/src/digest.rs b/atat/src/digest.rs
index 4edbbfbc..c1257faf 100644
--- a/atat/src/digest.rs
+++ b/atat/src/digest.rs
@@ -201,7 +201,7 @@ pub mod parser {
         branch::alt,
         bytes::streaming::tag,
         character::complete,
-        combinator::{eof, map, map_res, not, recognize},
+        combinator::{eof, map, map_res, recognize},
         error::ParseError,
         sequence::tuple,
         IResult,
@@ -256,6 +256,7 @@ pub mod parser {
                 )
             }),
             // Matches the equivalent of regex: "\r\n\+CME ERROR:\s*([^\n\r]+)\r\n"
+            #[cfg(feature = "string_errors")]
             map(string_error("\r\n+CME ERROR:"), |(error_msg, len)| {
                 (
                     DigestResult::Response(Err(InternalError::CmeError(CmeError::from_msg(
@@ -265,6 +266,7 @@ pub mod parser {
                 )
             }),
             // Matches the equivalent of regex: "\r\n\+CMS ERROR:\s*([^\n\r]+)\r\n"
+            #[cfg(feature = "string_errors")]
             map(string_error("\r\n+CMS ERROR:"), |(error_msg, len)| {
                 (
                     DigestResult::Response(Err(InternalError::CmsError(CmsError::from_msg(
@@ -397,6 +399,7 @@ pub mod parser {
     }
 
     /// Matches the equivalent of regex: "{token}\s*([^\n\r]+)\r\n"
+    #[cfg(feature = "string_errors")]
     fn string_error<'a, T, Error: ParseError<&'a [u8]>>(
         token: T,
     ) -> impl Fn(&'a [u8]) -> IResult<&'a [u8], (&'a [u8], usize), Error>
@@ -407,7 +410,7 @@ pub mod parser {
         move |i| {
             let (i, (prefix_data, _, error_msg)) = tuple((
                 recognize(take_until_including(token.clone())),
-                not(tag("\r")),
+                nom::combinator::not(tag("\r")),
                 recognize(take_until_including("\r\n")),
             ))(i)?;
 
@@ -554,6 +557,7 @@ mod test {
     }
 
     #[test]
+    #[cfg(feature = "string_errors")]
     fn mm_error() {
         let tests: Vec<(&[u8], DigestResult, usize)> = vec![
             (b"\r\nUNKNOWN COMMAND\r\n", DigestResult::None, 0),
@@ -1044,6 +1048,7 @@ mod test {
     }
 
     #[test]
+    #[cfg(feature = "string_errors")]
     fn verbose_error_response() {
         let mut digester = AtDigester::<UrcTestParser>::new();
         let mut buf = heapless::Vec::<u8, TEST_RX_BUF_LEN>::new();
diff --git a/atat/src/error/cme_error.rs b/atat/src/error/cme_error.rs
index 6d41f77d..6ff74066 100644
--- a/atat/src/error/cme_error.rs
+++ b/atat/src/error/cme_error.rs
@@ -502,6 +502,7 @@ impl From<u16> for CmeError {
     }
 }
 
+#[cfg(feature = "string_errors")]
 impl CmeError {
     pub const fn from_msg(s: &[u8]) -> Self {
         // FIXME:
diff --git a/atat/src/error/cms_error.rs b/atat/src/error/cms_error.rs
index 2231da88..e8838927 100644
--- a/atat/src/error/cms_error.rs
+++ b/atat/src/error/cms_error.rs
@@ -84,6 +84,7 @@ impl From<u16> for CmsError {
     }
 }
 
+#[cfg(feature = "string_errors")]
 impl CmsError {
     pub const fn from_msg(s: &[u8]) -> Self {
         // FIXME: