diff --git a/cranelift/codegen/src/data_value.rs b/cranelift/codegen/src/data_value.rs
index 965ce1bec5..13aa237674 100644
--- a/cranelift/codegen/src/data_value.rs
+++ b/cranelift/codegen/src/data_value.rs
@@ -86,6 +86,7 @@ impl DataValue {
             DataValue::I16(i) => dst[..2].copy_from_slice(&i.to_ne_bytes()[..]),
             DataValue::I32(i) => dst[..4].copy_from_slice(&i.to_ne_bytes()[..]),
             DataValue::I64(i) => dst[..8].copy_from_slice(&i.to_ne_bytes()[..]),
+            DataValue::I128(i) => dst[..16].copy_from_slice(&i.to_ne_bytes()[..]),
             DataValue::F32(f) => dst[..4].copy_from_slice(&f.bits().to_ne_bytes()[..]),
             DataValue::F64(f) => dst[..8].copy_from_slice(&f.bits().to_ne_bytes()[..]),
             DataValue::V128(v) => dst[..16].copy_from_slice(&v[..]),
@@ -104,6 +105,7 @@ impl DataValue {
             types::I16 => DataValue::I16(i16::from_ne_bytes(src[..2].try_into().unwrap())),
             types::I32 => DataValue::I32(i32::from_ne_bytes(src[..4].try_into().unwrap())),
             types::I64 => DataValue::I64(i64::from_ne_bytes(src[..8].try_into().unwrap())),
+            types::I128 => DataValue::I128(i128::from_ne_bytes(src[..16].try_into().unwrap())),
             types::F32 => DataValue::F32(Ieee32::with_bits(u32::from_ne_bytes(
                 src[..4].try_into().unwrap(),
             ))),
diff --git a/cranelift/reader/src/parser.rs b/cranelift/reader/src/parser.rs
index 97b4a7c77d..a0e5a35e3a 100644
--- a/cranelift/reader/src/parser.rs
+++ b/cranelift/reader/src/parser.rs
@@ -921,6 +921,49 @@ impl<'a> Parser<'a> {
         }
     }
 
+    // Match and consume an i128 immediate.
+    fn match_imm128(&mut self, err_msg: &str) -> ParseResult<i128> {
+        if let Some(Token::Integer(text)) = self.token() {
+            self.consume();
+            let negative = text.starts_with('-');
+            let positive = text.starts_with('+');
+            let text = if negative || positive {
+                // Strip sign prefix.
+                &text[1..]
+            } else {
+                text
+            };
+
+            // Parse the text value; the lexer gives us raw text that looks like an integer.
+            let value = if text.starts_with("0x") {
+                // Skip underscores.
+                let text = text.replace("_", "");
+                // Parse it as a i128 in hexadecimal form.
+                u128::from_str_radix(&text[2..], 16)
+                    .map_err(|_| self.error("unable to parse i128 as a hexadecimal immediate"))?
+            } else {
+                // Parse it as a i128 to check for overflow and other issues.
+                text.parse()
+                    .map_err(|_| self.error("expected i128 decimal immediate"))?
+            };
+
+            // Apply sign if necessary.
+            let signed = if negative {
+                let value = value.wrapping_neg() as i128;
+                if value > 0 {
+                    return Err(self.error("negative number too small"));
+                }
+                value
+            } else {
+                value as i128
+            };
+
+            Ok(signed)
+        } else {
+            err!(self.loc, err_msg)
+        }
+    }
+
     // Match and consume an optional offset32 immediate.
     //
     // Note that this will match an empty string as an empty offset, and that if an offset is
@@ -2805,6 +2848,7 @@ impl<'a> Parser<'a> {
             I16 => DataValue::from(self.match_imm16("expected an i16")?),
             I32 => DataValue::from(self.match_imm32("expected an i32")?),
             I64 => DataValue::from(Into::<i64>::into(self.match_imm64("expected an i64")?)),
+            I128 => DataValue::from(self.match_imm128("expected an i64")?),
             F32 => DataValue::from(self.match_ieee32("expected an f32")?),
             F64 => DataValue::from(self.match_ieee64("expected an f64")?),
             _ if ty.is_vector() => {
@@ -4126,6 +4170,11 @@ mod tests {
         assert_eq!(parse("16", I16).to_string(), "16");
         assert_eq!(parse("32", I32).to_string(), "32");
         assert_eq!(parse("64", I64).to_string(), "64");
+        assert_eq!(
+            parse("0x01234567_01234567_01234567_01234567", I128).to_string(),
+            "1512366032949150931280199141537564007"
+        );
+        assert_eq!(parse("1234567", I128).to_string(), "1234567");
         assert_eq!(parse("0x32.32", F32).to_string(), "0x1.919000p5");
         assert_eq!(parse("0x64.64", F64).to_string(), "0x1.9190000000000p6");
         assert_eq!(parse("true", B1).to_string(), "true");