diff --git a/compiler/src/dotty/tools/dotc/typer/Inliner.scala b/compiler/src/dotty/tools/dotc/typer/Inliner.scala
index 70861d4be87c..41d3eefaa321 100644
--- a/compiler/src/dotty/tools/dotc/typer/Inliner.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Inliner.scala
@@ -1035,7 +1035,7 @@ class Inliner(call: tpd.Tree, rhsToInline: tpd.Tree)(implicit ctx: Context) {
               case _ => false
             }
           }
-          if (guardOK) Some((caseBindings, cdef.body.subst(from, to)))
+          if (guardOK) Some((caseBindings.map(_.subst(from, to)), cdef.body.subst(from, to)))
           else None
         }
         else None
@@ -1135,7 +1135,6 @@ class Inliner(call: tpd.Tree, rhsToInline: tpd.Tree)(implicit ctx: Context) {
                 }
               case _ => rhs0
             }
-
             val (usedBindings, rhs2) = dropUnusedDefs(caseBindings, rhs1)
             val rhs = seq(usedBindings, rhs2)
             inlining.println(i"""--- reduce:
diff --git a/tests/pos/i7878.scala b/tests/pos/i7878.scala
new file mode 100644
index 000000000000..d47bb32f1a65
--- /dev/null
+++ b/tests/pos/i7878.scala
@@ -0,0 +1,15 @@
+object Boom {
+  import scala.compiletime._
+  trait Fail[A <: Int, B <: Int]
+
+  erased inline given fail[X <: Int, Y <: Int]: Fail[X, Y] = {
+     scala.compiletime.summonFrom {
+       case t: Fail[X, y] if constValue[y] < constValue[Y] => ???
+    }
+  }
+
+  val a: Int = 1
+  given ev1: Fail[a.type, 2] = null
+
+  summon[Fail[a.type, 3]]
+}
\ No newline at end of file