diff --git a/Cargo.toml b/Cargo.toml
index 49e2c07..0e22e24 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,7 +7,7 @@ description = "Port of biocommons/hgvs to Rust"
 license = "Apache-2.0"
 repository = "https://github.com/varfish-org/hgvs-rs"
 readme = "README.md"
-rust-version = "1.77.0"
+rust-version = "1.80.0"
 
 [lib]
 name = "hgvs"
diff --git a/build.rs b/build.rs
index 14789f0..2be8998 100644
--- a/build.rs
+++ b/build.rs
@@ -16,6 +16,7 @@ fn main() -> Result<()> {
     generate_codon_2bit_to_aa1_chrmt_vertebrate(&mut f)?;
 
     generate_aa1_to_aa3_str_lookup_function(&mut f)?;
+    generate_aa1_to_aa3_str_lookup_table(&mut f)?;
     generate_aa3_to_aa1_lookup_function(&mut f)?;
 
     f.flush()?;
@@ -95,7 +96,10 @@ fn generate_codon_2bit_to_aa1_chrmt_vertebrate(f: &mut BufWriter<File>) -> Resul
 }
 
 fn generate_aa1_to_aa3_str_lookup_function(f: &mut BufWriter<File>) -> Result<()> {
-    writeln!(f, "fn _aa1_to_aa3_str(aa1: u8) -> Option<&'static str> {{")?;
+    writeln!(
+        f,
+        "const fn _aa1_to_aa3_str(aa1: u8) -> Option<&'static str> {{"
+    )?;
     writeln!(f, "    match aa1 {{")?;
     for (aa3, aa1) in AA3_TO_AA1_VEC {
         writeln!(f, "        b'{}' => Some(\"{}\"),", aa1, aa3)?;
@@ -106,8 +110,25 @@ fn generate_aa1_to_aa3_str_lookup_function(f: &mut BufWriter<File>) -> Result<()
     Ok(())
 }
 
+fn generate_aa1_to_aa3_str_lookup_table(f: &mut BufWriter<File>) -> Result<()> {
+    let mut result = [""; 256];
+    for (aa3, aa1) in AA3_TO_AA1_VEC {
+        result[aa1.as_bytes()[0] as usize] = aa3;
+    }
+    write!(f, "const AA1_TO_AA3_STR: [Option<&str>; 256] = [")?;
+    for v in result {
+        if v.is_empty() {
+            write!(f, "None, ")?;
+        } else {
+            write!(f, r##"Some("{}"), "##, v)?;
+        }
+    }
+    writeln!(f, "];")?;
+    Ok(())
+}
+
 fn generate_aa3_to_aa1_lookup_function(f: &mut BufWriter<File>) -> Result<()> {
-    writeln!(f, "fn _aa3_to_aa1(aa3: &[u8]) -> Option<u8> {{")?;
+    writeln!(f, "const fn _aa3_to_aa1(aa3: &[u8]) -> Option<u8> {{")?;
     writeln!(f, "    match aa3 {{")?;
     for (aa3, aa1) in AA3_TO_AA1_VEC {
         writeln!(f, "        b\"{}\" => Some(b'{}'),", aa3, aa1)?;
diff --git a/src/sequences.rs b/src/sequences.rs
index a44fd83..238ce2e 100644
--- a/src/sequences.rs
+++ b/src/sequences.rs
@@ -167,7 +167,7 @@ pub fn aa1_to_aa3(seq: &str) -> Result<String, Error> {
     let mut result = String::with_capacity(seq.len() * 3);
 
     for (i, aa1) in seq.as_bytes().iter().enumerate() {
-        let aa3 = _aa1_to_aa3_str(*aa1).ok_or_else(|| {
+        let aa3 = AA1_TO_AA3_STR[*aa1 as usize].ok_or_else(|| {
             Error::InvalidOneLetterAminoAcid(format!("{:?}", aa1), format!("{}", i + 1))
         })?;
         result.push_str(aa3);