diff --git a/tsc/internal/fourslash/tests/contentMapperInlayHints_test.go b/tsc/internal/fourslash/tests/contentMapperInlayHints_test.go
new file mode 100644
index 0000000000000..63607c844cc15
--- /dev/null
+++ b/tsc/internal/fourslash/tests/contentMapperInlayHints_test.go
@@ -0,0 +1,27 @@
+package fourslash_test
+
+import (
+	"testing"
+
+	"github.com/microsoft/TypeScript/tsc/internal/ls/lsutil"
+	"github.com/microsoft/TypeScript/tsc/internal/testutil"
+	"github.com/microsoft/TypeScript/tsc/internal/testutil/contentmappertest"
+)
+
+func TestContentMapperInlayHints(t *testing.T) {
+	t.Parallel()
+	defer testutil.RecoverAndFail(t, "Panic on fourslash test")
+	// original: (+ 1 2 "oops")
+	// virtual:  add(1, 2, "oops");
+	//           [-) [) [) [----) mapped spans
+	f, done := newContentMapperFourslash(t, `// @Filename: /app.lisp
+(+ 1 2 "oops")
+
+// @Filename: /main.ts
+declare function add(a: number, b: number, c: string): number;
+`, contentmappertest.LispMapper, ".lisp")
+	defer done()
+
+	f.GoToFile(t, "/app.lisp")
+	f.VerifyBaselineInlayHints(t, nil /*span*/, &lsutil.UserPreferences{InlayHints: lsutil.InlayHintsPreferences{IncludeInlayParameterNameHints: lsutil.IncludeInlayParameterNameHintsAll}})
+}
diff --git a/tsc/internal/ls/inlay_hints.go b/tsc/internal/ls/inlay_hints.go
index 0864f8df361e7..ab1b04646ac42 100644
--- a/tsc/internal/ls/inlay_hints.go
+++ b/tsc/internal/ls/inlay_hints.go
@@ -12,6 +12,7 @@ import (
 	"github.com/microsoft/TypeScript/tsc/internal/core"
 	"github.com/microsoft/TypeScript/tsc/internal/debug"
 	"github.com/microsoft/TypeScript/tsc/internal/evaluator"
+	"github.com/microsoft/TypeScript/tsc/internal/json"
 	"github.com/microsoft/TypeScript/tsc/internal/ls/lsconv"
 	"github.com/microsoft/TypeScript/tsc/internal/ls/lsutil"
 	"github.com/microsoft/TypeScript/tsc/internal/lsp/lsproto"
@@ -37,6 +38,10 @@ func (l *LanguageService) ProvideInlayHint(
 
 	mappedRanges := l.converters.FromLSPRangeIntersectingForSourceFile(file, params.Range, spanmap.FeatureInlayHints)
 	result := make([]*lsproto.InlayHint, 0, len(mappedRanges))
+	var seen map[string]struct{}
+	if len(mappedRanges) > 1 {
+		seen = make(map[string]struct{})
+	}
 	for _, mapped := range mappedRanges {
 		projection := mapped.Script
 		checker, done := program.GetTypeCheckerForFile(ctx, projection)
@@ -51,7 +56,22 @@ func (l *LanguageService) ProvideInlayHint(
 			converters:      l.converters,
 		}
 		inlayHintState.visit(projection.AsNode())
-		result = append(result, inlayHintState.result...)
+		if seen == nil {
+			result = append(result, inlayHintState.result...)
+			continue
+		}
+		for _, hint := range inlayHintState.result {
+			encoded, err := json.Marshal(hint)
+			if err != nil {
+				return lsproto.InlayHintsOrNull{}, err
+			}
+			key := string(encoded)
+			if _, ok := seen[key]; ok {
+				continue
+			}
+			seen[key] = struct{}{}
+			result = append(result, hint)
+		}
 	}
 	return lsproto.InlayHintsOrNull{InlayHints: &result}, nil
 }
diff --git a/tsc/testdata/baselines/reference/fourslash/inlayHints/contentMapperInlayHints.baseline b/tsc/testdata/baselines/reference/fourslash/inlayHints/contentMapperInlayHints.baseline
new file mode 100644
index 0000000000000..8ffd06588c5bb
--- /dev/null
+++ b/tsc/testdata/baselines/reference/fourslash/inlayHints/contentMapperInlayHints.baseline
@@ -0,0 +1,96 @@
+// === Inlay Hints ===
+(+ 1 2 "oops")
+   ^
+{
+  "position": {
+    "line": 0,
+    "character": 3
+  },
+  "label": [
+    {
+      "value": "a",
+      "location": {
+        "uri": "file:///main.ts",
+        "range": {
+          "start": {
+            "line": 0,
+            "character": 21
+          },
+          "end": {
+            "line": 0,
+            "character": 22
+          }
+        }
+      }
+    },
+    {
+      "value": ":"
+    }
+  ],
+  "kind": 2,
+  "paddingRight": true
+}
+
+(+ 1 2 "oops")
+     ^
+{
+  "position": {
+    "line": 0,
+    "character": 5
+  },
+  "label": [
+    {
+      "value": "b",
+      "location": {
+        "uri": "file:///main.ts",
+        "range": {
+          "start": {
+            "line": 0,
+            "character": 32
+          },
+          "end": {
+            "line": 0,
+            "character": 33
+          }
+        }
+      }
+    },
+    {
+      "value": ":"
+    }
+  ],
+  "kind": 2,
+  "paddingRight": true
+}
+
+(+ 1 2 "oops")
+       ^
+{
+  "position": {
+    "line": 0,
+    "character": 7
+  },
+  "label": [
+    {
+      "value": "c",
+      "location": {
+        "uri": "file:///main.ts",
+        "range": {
+          "start": {
+            "line": 0,
+            "character": 43
+          },
+          "end": {
+            "line": 0,
+            "character": 44
+          }
+        }
+      }
+    },
+    {
+      "value": ":"
+    }
+  ],
+  "kind": 2,
+  "paddingRight": true
+}
\ No newline at end of file