diff --git a/compiler/src/dotty/tools/dotc/sbt/package.scala b/compiler/src/dotty/tools/dotc/sbt/package.scala
index 379a2e45ce40..dc0df381f08f 100644
--- a/compiler/src/dotty/tools/dotc/sbt/package.scala
+++ b/compiler/src/dotty/tools/dotc/sbt/package.scala
@@ -4,6 +4,7 @@ import dotty.tools.dotc.core.Contexts.Context
 import dotty.tools.dotc.core.Symbols.Symbol
 import dotty.tools.dotc.core.NameOps.stripModuleClassSuffix
 import dotty.tools.dotc.core.Names.Name
+import dotty.tools.dotc.core.Names.termName
 
 inline val TermNameHash = 1987 // 300th prime
 inline val TypeNameHash = 1993 // 301st prime
@@ -11,10 +12,15 @@ inline val InlineParamHash = 1997 // 302nd prime
 
 extension (sym: Symbol)
 
-  def constructorName(using Context) =
-    sym.owner.fullName ++ ";init;"
-
-  /** Mangle a JVM symbol name in a format better suited for internal uses by sbt. */
-  def zincMangledName(using Context): Name =
-    if (sym.isConstructor) constructorName
-    else sym.name.stripModuleClassSuffix
+  /** Mangle a JVM symbol name in a format better suited for internal uses by sbt.
+   *  WARNING: output must not be written to TASTy, as it is not a valid TASTy name.
+   */
+  private[sbt] def zincMangledName(using Context): Name =
+    if sym.isConstructor then
+      // TODO: ideally we should avoid unnecessarily caching these Zinc specific
+      // names in the global chars array. But we would need to restructure
+      // ExtractDependencies caches to avoid expensive `toString` on
+      // each member reference.
+      termName(sym.owner.fullName.mangledString.replace(".", ";").nn ++ ";init;")
+    else
+      sym.name.stripModuleClassSuffix
diff --git a/sbt-bridge/test/xsbt/ExtractUsedNamesSpecification.scala b/sbt-bridge/test/xsbt/ExtractUsedNamesSpecification.scala
index 2b2b7d26c716..e47371175de6 100644
--- a/sbt-bridge/test/xsbt/ExtractUsedNamesSpecification.scala
+++ b/sbt-bridge/test/xsbt/ExtractUsedNamesSpecification.scala
@@ -306,7 +306,7 @@ class ExtractUsedNamesSpecification {
     // All classes extend Object
     "Object",
     // All classes have a default constructor called <init>
-    "java.lang.Object;init;",
+    "java;lang;Object;init;",
     // the return type of the default constructor is Unit
     "Unit"
   )
diff --git a/sbt-test/source-dependencies/constructors/A.scala b/sbt-test/source-dependencies/constructors/A.scala
index b81025bada4d..0c5a5efa5b25 100644
--- a/sbt-test/source-dependencies/constructors/A.scala
+++ b/sbt-test/source-dependencies/constructors/A.scala
@@ -1 +1,3 @@
+package example
+
 class A(a: Int)
diff --git a/sbt-test/source-dependencies/constructors/B.scala b/sbt-test/source-dependencies/constructors/B.scala
index e44b1d4c7852..b66f04320f13 100644
--- a/sbt-test/source-dependencies/constructors/B.scala
+++ b/sbt-test/source-dependencies/constructors/B.scala
@@ -1 +1,3 @@
+package example
+
 class B { val y = new A(2) }
diff --git a/sbt-test/source-dependencies/constructors/changes/A2.scala b/sbt-test/source-dependencies/constructors/changes/A2.scala
index edd9e160e7bf..5f72892e6f26 100644
--- a/sbt-test/source-dependencies/constructors/changes/A2.scala
+++ b/sbt-test/source-dependencies/constructors/changes/A2.scala
@@ -1 +1,3 @@
+package example
+
 class A(a: String)
diff --git a/sbt-test/source-dependencies/constructors/changes/B2.scala b/sbt-test/source-dependencies/constructors/changes/B2.scala
index 701f0514685f..7b1399a8ac49 100644
--- a/sbt-test/source-dependencies/constructors/changes/B2.scala
+++ b/sbt-test/source-dependencies/constructors/changes/B2.scala
@@ -1 +1,3 @@
+package example
+
 class B { val y = new A("a") }