diff --git a/src/decode.rs b/src/decode.rs
index 30a4e3b..b1a9657 100644
--- a/src/decode.rs
+++ b/src/decode.rs
@@ -3,6 +3,7 @@
 use std::sync::Arc;
 
 use crate::error::{Error, Result};
+use crate::token::INVALID_ID;
 use crate::{SourceMap, Token};
 
 /// See <https://github.com/tc39/source-map/blob/1930e58ffabefe54038f7455759042c6e3dd590e/source-map-rev3.md>.
@@ -80,8 +81,8 @@ fn decode_mapping(mapping: &str, names_len: usize, sources_len: usize) -> Result
             parse_vlq_segment_into(segment, &mut nums)?;
             dst_col = (i64::from(dst_col) + nums[0]) as u32;
 
-            let mut src = !0;
-            let mut name = !0;
+            let mut src = INVALID_ID;
+            let mut name = INVALID_ID;
 
             if nums.len() > 1 {
                 if nums.len() != 4 && nums.len() != 5 {
@@ -110,8 +111,8 @@ fn decode_mapping(mapping: &str, names_len: usize, sources_len: usize) -> Result
                 dst_col,
                 src_line,
                 src_col,
-                if src == !0 { None } else { Some(src) },
-                if name == !0 { None } else { Some(name) },
+                if src == INVALID_ID { None } else { Some(src) },
+                if name == INVALID_ID { None } else { Some(name) },
             ));
         }
     }
diff --git a/src/token.rs b/src/token.rs
index 26f8dea..50873e4 100644
--- a/src/token.rs
+++ b/src/token.rs
@@ -2,6 +2,10 @@ use std::sync::Arc;
 
 use crate::SourceMap;
 
+/// Sentinel value representing an invalid/missing ID for source or name.
+/// Used when a token doesn't have an associated source file or name.
+pub(crate) const INVALID_ID: u32 = u32::MAX;
+
 /// The `Token` is used to generate vlq `mappings`.
 #[derive(Debug, PartialEq, Eq, Clone, Copy)]
 pub struct Token {
@@ -27,8 +31,8 @@ impl Token {
             dst_col,
             src_line,
             src_col,
-            source_id: source_id.unwrap_or(!0),
-            name_id: name_id.unwrap_or(!0),
+            source_id: source_id.unwrap_or(INVALID_ID),
+            name_id: name_id.unwrap_or(INVALID_ID),
         }
     }
 
@@ -49,11 +53,11 @@ impl Token {
     }
 
     pub fn get_name_id(&self) -> Option<u32> {
-        if self.name_id == !0 { None } else { Some(self.name_id) }
+        if self.name_id == INVALID_ID { None } else { Some(self.name_id) }
     }
 
     pub fn get_source_id(&self) -> Option<u32> {
-        if self.source_id == !0 { None } else { Some(self.source_id) }
+        if self.source_id == INVALID_ID { None } else { Some(self.source_id) }
     }
 }
 
@@ -123,19 +127,23 @@ impl<'a> SourceViewToken<'a> {
     }
 
     pub fn get_name_id(&self) -> Option<u32> {
-        if self.token.name_id == !0 { None } else { Some(self.token.name_id) }
+        if self.token.name_id == INVALID_ID { None } else { Some(self.token.name_id) }
     }
 
     pub fn get_source_id(&self) -> Option<u32> {
-        if self.token.source_id == !0 { None } else { Some(self.token.source_id) }
+        if self.token.source_id == INVALID_ID { None } else { Some(self.token.source_id) }
     }
 
     pub fn get_name(&self) -> Option<&Arc<str>> {
-        if self.token.name_id == !0 { None } else { self.sourcemap.get_name(self.token.name_id) }
+        if self.token.name_id == INVALID_ID {
+            None
+        } else {
+            self.sourcemap.get_name(self.token.name_id)
+        }
     }
 
     pub fn get_source(&self) -> Option<&Arc<str>> {
-        if self.token.source_id == !0 {
+        if self.token.source_id == INVALID_ID {
             None
         } else {
             self.sourcemap.get_source(self.token.source_id)
@@ -143,7 +151,7 @@ impl<'a> SourceViewToken<'a> {
     }
 
     pub fn get_source_content(&self) -> Option<&Arc<str>> {
-        if self.token.source_id == !0 {
+        if self.token.source_id == INVALID_ID {
             None
         } else {
             self.sourcemap.get_source_content(self.token.source_id)
@@ -151,7 +159,7 @@ impl<'a> SourceViewToken<'a> {
     }
 
     pub fn get_source_and_content(&self) -> Option<(&Arc<str>, &Arc<str>)> {
-        if self.token.source_id == !0 {
+        if self.token.source_id == INVALID_ID {
             None
         } else {
             self.sourcemap.get_source_and_content(self.token.source_id)