diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6465b46a141..aef578926a4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+* Fill in `null` entries in input source maps ([#3144](https://github.com/evanw/esbuild/issues/3144))
+
+    If esbuild bundles input files with source maps and those source maps contain a `sourcesContent` array with `null` entries, esbuild previously copied those `null` entries over to the output source map. With this release, esbuild will now attempt to fill in those `null` entries by looking for a file on the file system with the corresponding name from the `sources` array. This matches esbuild's existing behavior that automatically generates the `sourcesContent` array from the file system if the entire `sourcesContent` array is missing.
+
 ## 0.18.0
 
 **This release deliberately contains backwards-incompatible changes.** To avoid automatically picking up releases like this, you should either be pinning the exact version of `esbuild` in your `package.json` file (recommended) or be using a version range syntax that only accepts patch upgrades such as `^0.17.0` or `~0.17.0`. See npm's documentation about [semver](https://docs.npmjs.com/cli/v6/using-npm/semver/) for more information.
diff --git a/internal/bundler/bundler.go b/internal/bundler/bundler.go
index 2d6e2b3c51c..ee31eaf2c12 100644
--- a/internal/bundler/bundler.go
+++ b/internal/bundler/bundler.go
@@ -480,23 +480,33 @@ func parseFile(args parseArgs) {
 						}
 					}
 
-					// If "sourcesContent" isn't present, try filling it in using the file system
-					if sourceMap != nil && sourceMap.SourcesContent == nil && !args.options.ExcludeSourcesContent {
-						for _, source := range sourceMap.Sources {
-							var absPath string
-							if args.fs.IsAbs(source) {
-								absPath = source
-							} else if path.Namespace == "file" {
-								absPath = args.fs.Join(args.fs.Dir(path.Text), source)
-							} else {
-								sourceMap.SourcesContent = append(sourceMap.SourcesContent, sourcemap.SourceContent{})
-								continue
-							}
-							var sourceContent sourcemap.SourceContent
-							if contents, err, _ := args.caches.FSCache.ReadFile(args.fs, absPath); err == nil {
-								sourceContent.Value = helpers.StringToUTF16(contents)
+					// If "sourcesContent" entries aren't present, try filling them in
+					// using the file system. This includes both generating the entire
+					// "sourcesContent" array if it's absent as well as filling in
+					// individual null entries in the array if the array is present.
+					if sourceMap != nil && !args.options.ExcludeSourcesContent {
+						// Make sure "sourcesContent" is big enough
+						if len(sourceMap.SourcesContent) < len(sourceMap.Sources) {
+							slice := make([]sourcemap.SourceContent, len(sourceMap.Sources))
+							copy(slice, sourceMap.SourcesContent)
+							sourceMap.SourcesContent = slice
+						}
+
+						// Attempt to fill in null entries using the file system
+						for i, source := range sourceMap.Sources {
+							if sourceMap.SourcesContent[i].Value == nil {
+								var absPath string
+								if args.fs.IsAbs(source) {
+									absPath = source
+								} else if path.Namespace == "file" {
+									absPath = args.fs.Join(args.fs.Dir(path.Text), source)
+								} else {
+									continue
+								}
+								if contents, err, _ := args.caches.FSCache.ReadFile(args.fs, absPath); err == nil {
+									sourceMap.SourcesContent[i].Value = helpers.StringToUTF16(contents)
+								}
 							}
-							sourceMap.SourcesContent = append(sourceMap.SourcesContent, sourceContent)
 						}
 					}
 
diff --git a/scripts/verify-source-map.js b/scripts/verify-source-map.js
index da1becd831f..40b66f89752 100644
--- a/scripts/verify-source-map.js
+++ b/scripts/verify-source-map.js
@@ -402,6 +402,34 @@ const toSearchMissingSourcesContent = {
   bar: 'src/foo.ts',
 }
 
+// The "null" should be filled in by the contents of "bar.ts"
+const testCaseNullSourcesContent = {
+  'entry.js': `import './foo.js'\n`,
+  'foo.ts': `import './bar.ts'\nconsole.log("foo")`,
+  'bar.ts': `console.log("bar")\n`,
+  'foo.js': `(() => {
+  // bar.ts
+  console.log("bar");
+
+  // foo.ts
+  console.log("foo");
+})();
+//# sourceMappingURL=foo.js.map
+`,
+  'foo.js.map': `{
+  "version": 3,
+  "sources": ["bar.ts", "foo.ts"],
+  "sourcesContent": [null, "import './bar.ts'\\nconsole.log(\\"foo\\")"],
+  "mappings": ";;AAAA,UAAQ,IAAI,KAAK;;;ACCjB,UAAQ,IAAI,KAAK;",
+  "names": []
+}
+`,
+}
+
+const toSearchNullSourcesContent = {
+  bar: 'bar.ts',
+}
+
 async function check(kind, testCase, toSearch, { ext, flags, entryPoints, crlf, followUpFlags = [] }) {
   let failed = 0
 
@@ -856,13 +884,21 @@ async function main() {
           crlf,
         }),
 
-        // Checks for loading missing sources content in nested source maps
+        // Checks for loading missing "sourcesContent" in nested source maps
         check('missing-sources-content' + suffix, testCaseMissingSourcesContent, toSearchMissingSourcesContent, {
           ext: 'js',
           flags: flags.concat('--outfile=out.js', '--bundle'),
           entryPoints: ['foo.js'],
           crlf,
         }),
+
+        // Checks for null entries in "sourcesContent" in nested source maps
+        check('null-sources-content' + suffix, testCaseNullSourcesContent, toSearchNullSourcesContent, {
+          ext: 'js',
+          flags: flags.concat('--outfile=out.js', '--bundle'),
+          entryPoints: ['foo.js'],
+          crlf,
+        }),
       )
     }
   }