diff --git a/compiler/src/dotty/tools/dotc/typer/Inferencing.scala b/compiler/src/dotty/tools/dotc/typer/Inferencing.scala
index fd8507a7d961..ed37a869d612 100644
--- a/compiler/src/dotty/tools/dotc/typer/Inferencing.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Inferencing.scala
@@ -205,7 +205,7 @@ object Inferencing {
     private def instantiate(tvar: TypeVar, fromBelow: Boolean): Boolean =
       if fromBelow && force.canImprove(tvar) then
         val inst = tvar.typeToInstantiateWith(fromBelow = true)
-        if apply(true, inst) then
+        if isFullyDefined(inst, ForceDegree.none) then
           // need to recursively check before improving, since improving adds type vars
           // which should not be instantiated at this point
           val better = improve(tvar)(inst)
diff --git a/tests/pos/i19637.scala b/tests/pos/i19637.scala
new file mode 100644
index 000000000000..53e609407bd0
--- /dev/null
+++ b/tests/pos/i19637.scala
@@ -0,0 +1,11 @@
+import java.util.stream.*
+import java.util.function.*
+
+val map: java.util.Map[String, String] = Stream.of("1", "2", "3").collect(Collectors.toMap(
+  (s: String) => s,
+  Function.identity(),
+  {
+    case ("1", "1") => "1"
+    case (_, l) => l
+  }
+))