diff --git a/compiler/test/dotty/tools/dotc/core/tasty/TastyHeaderUnpicklerTest.scala b/compiler/test/dotty/tools/dotc/core/tasty/TastyHeaderUnpicklerTest.scala
index c722af979d76..53c1f40638a4 100644
--- a/compiler/test/dotty/tools/dotc/core/tasty/TastyHeaderUnpicklerTest.scala
+++ b/compiler/test/dotty/tools/dotc/core/tasty/TastyHeaderUnpicklerTest.scala
@@ -56,7 +56,7 @@ class TastyHeaderUnpicklerTest {
     val file = TastyVersion(28, 4, 1)
     val read = TastyVersion(28, 4, 0)
     expectUnpickleError(runTest(file, read, "Scala 3.4.0-RC1-bin-SNAPSHOT")) {
-      """TASTy file produced by Scala 3.4.0-RC1-bin-SNAPSHOT has a backward incompatible TASTy version 28.4-experimental-1,
+      """Backward incompatible TASTy file has version 28.4-experimental-1, produced by Scala 3.4.0-RC1-bin-SNAPSHOT,
         |  expected stable TASTy from 28.0 to 28.4.
         |  The source of this file should be recompiled by a Scala 3.4.0 compiler or newer.
         |  Usually this means that the library dependency containing this file should be updated.
@@ -70,7 +70,7 @@ class TastyHeaderUnpicklerTest {
     val file = TastyVersion(28, 3, 1)
     val read = TastyVersion(28, 4, 0)
     expectUnpickleError(runTest(file, read, "Scala 3.2.1-RC1-bin-SNAPSHOT")) {
-      """TASTy file produced by Scala 3.2.1-RC1-bin-SNAPSHOT has a backward incompatible TASTy version 28.3-experimental-1,
+      """Backward incompatible TASTy file has version 28.3-experimental-1, produced by Scala 3.2.1-RC1-bin-SNAPSHOT,
         |  expected stable TASTy from 28.0 to 28.4.
         |  The source of this file should be recompiled by a Scala 3.3.0 compiler or newer.
         |  Usually this means that the library dependency containing this file should be updated.
@@ -84,7 +84,7 @@ class TastyHeaderUnpicklerTest {
     val file = TastyVersion(27, 3, 0)
     val read = TastyVersion(28, 3, 0)
     expectUnpickleError(runTest(file, read, "Scala 3.0.0-M1")) {
-      """TASTy file has a backward incompatible TASTy version 27.3,
+      """Backward incompatible TASTy file has version 27.3,
         |  expected stable TASTy from 28.0 to 28.3.
         |  The source of this file should be recompiled by a Scala 3.0.0 compiler or newer.
         |  Usually this means that the library dependency containing this file should be updated.
@@ -99,7 +99,7 @@ class TastyHeaderUnpicklerTest {
     val file = TastyVersion(27, 3, 0)
     val read = TastyVersion(28, 3, 0)
     expectUnpickleError(runTest(file, read, "Scala 3.0.0-M1", generic = true)) {
-      """TASTy file has a backward incompatible TASTy version 27.3,
+      """Backward incompatible TASTy file has version 27.3,
         |  expected stable TASTy from 28.0 to 28.3.
         |  The source of this file should be recompiled by a later version.
         |  Usually this means that the classpath entry of this file should be updated.
@@ -113,7 +113,7 @@ class TastyHeaderUnpicklerTest {
     val file = TastyVersion(28, 4, 1)
     val read = TastyVersion(28, 4, 2)
     expectUnpickleError(runTest(file, read, "Scala 3.3.3-RC1-NIGHTLY")) {
-      """TASTy file produced by Scala 3.3.3-RC1-NIGHTLY has a backward incompatible TASTy version 28.4-experimental-1,
+      """Backward incompatible TASTy file has version 28.4-experimental-1, produced by Scala 3.3.3-RC1-NIGHTLY,
         |  expected stable TASTy from 28.0 to 28.3, or exactly 28.4-experimental-2.
         |  The source of this file should be recompiled by the same nightly or snapshot Scala 3.3 compiler.
         |  Usually this means that the library dependency containing this file should be updated.
@@ -128,7 +128,7 @@ class TastyHeaderUnpicklerTest {
     val file = TastyVersion(28, 4, 1)
     val read = TastyVersion(28, 4, 2)
     expectUnpickleError(runTest(file, read, "Scala 3.3.3-RC1-NIGHTLY", generic = true)) {
-      """TASTy file produced by Scala 3.3.3-RC1-NIGHTLY has a backward incompatible TASTy version 28.4-experimental-1,
+      """Backward incompatible TASTy file has version 28.4-experimental-1, produced by Scala 3.3.3-RC1-NIGHTLY,
         |  expected stable TASTy from 28.0 to 28.3, or exactly 28.4-experimental-2.
         |  The source of this file should be recompiled by a later version.
         |  Usually this means that the classpath entry of this file should be updated.
@@ -142,7 +142,7 @@ class TastyHeaderUnpicklerTest {
     val file = TastyVersion(28, 3, 0)
     val read = TastyVersion(28, 2, 0)
     expectUnpickleError(runTest(file, read, "Scala 3.3.1")) {
-      """TASTy file produced by Scala 3.3.1 has a forward incompatible TASTy version 28.3,
+      """Forward incompatible TASTy file has version 28.3, produced by Scala 3.3.1,
         |  expected stable TASTy from 28.0 to 28.2.
         |  To read this TASTy file, use a Scala 3.3.0 compiler or newer.
         |  Please refer to the documentation for information on TASTy versioning:
@@ -156,7 +156,7 @@ class TastyHeaderUnpicklerTest {
     val file = TastyVersion(28, 3, 0)
     val read = TastyVersion(28, 2, 0)
     expectUnpickleError(runTest(file, read, "Scala 3.3.1", generic = true)) {
-      """TASTy file produced by Scala 3.3.1 has a forward incompatible TASTy version 28.3,
+      """Forward incompatible TASTy file has version 28.3, produced by Scala 3.3.1,
         |  expected stable TASTy from 28.0 to 28.2.
         |  To read this TASTy file, use a newer version of this tool compatible with TASTy 28.3.
         |  Please refer to the documentation for information on TASTy versioning:
@@ -169,7 +169,7 @@ class TastyHeaderUnpicklerTest {
     val file = TastyVersion(28, 3, 1)
     val read = TastyVersion(28, 2, 0)
     expectUnpickleError(runTest(file, read, "Scala 3.2.2-RC1-NIGHTLY")) {
-      """TASTy file produced by Scala 3.2.2-RC1-NIGHTLY has a forward incompatible TASTy version 28.3-experimental-1,
+      """Forward incompatible TASTy file has version 28.3-experimental-1, produced by Scala 3.2.2-RC1-NIGHTLY,
         |  expected stable TASTy from 28.0 to 28.2.
         |  To read this experimental TASTy file, use the same nightly or snapshot Scala 3.2 compiler.
         |  Note that you are using a stable compiler, which can not read experimental TASTy.
@@ -183,7 +183,7 @@ class TastyHeaderUnpicklerTest {
     val file = TastyVersion(29, 0, 0)
     val read = TastyVersion(28, 3, 0)
     expectUnpickleError(runTest(file, read, "Scala 4.0.0")) {
-      """TASTy file produced by Scala 4.0.0 has a forward incompatible TASTy version 29.0,
+      """Forward incompatible TASTy file has version 29.0, produced by Scala 4.0.0,
         |  expected stable TASTy from 28.0 to 28.3.
         |  To read this TASTy file, use a more recent Scala compiler.
         |  Please refer to the documentation for information on TASTy versioning:
@@ -196,7 +196,7 @@ class TastyHeaderUnpicklerTest {
     val file = TastyVersion(29, 0, 1)
     val read = TastyVersion(28, 3, 0)
     expectUnpickleError(runTest(file, read, "Scala 4.0.0-M1")) {
-      """TASTy file produced by Scala 4.0.0-M1 has a forward incompatible TASTy version 29.0-experimental-1,
+      """Forward incompatible TASTy file has version 29.0-experimental-1, produced by Scala 4.0.0-M1,
         |  expected stable TASTy from 28.0 to 28.3.
         |  To read this experimental TASTy file, use the same Scala compiler.
         |  Note that you are using a stable compiler, which can not read experimental TASTy.
@@ -211,7 +211,7 @@ class TastyHeaderUnpicklerTest {
     val file = TastyVersion(29, 0, 1)
     val read = TastyVersion(28, 3, 0)
     expectUnpickleError(runTest(file, read, "Scala 4.0.0-M1", generic = true)) {
-      """TASTy file produced by Scala 4.0.0-M1 has a forward incompatible TASTy version 29.0-experimental-1,
+      """Forward incompatible TASTy file has version 29.0-experimental-1, produced by Scala 4.0.0-M1,
         |  expected stable TASTy from 28.0 to 28.3.
         |  To read this experimental TASTy file, use the version of this tool compatible with TASTy 29.0-experimental-1.
         |  Note that this tool does not support reading experimental TASTy.
@@ -225,7 +225,7 @@ class TastyHeaderUnpicklerTest {
     val file = TastyVersion(28, 4, 0)
     val read = TastyVersion(28, 4, 1) // 3.4.0-RC1-NIGHTLY
     expectUnpickleError(runTest(file, read, "Scala 3.4.2")) {
-      """TASTy file produced by Scala 3.4.2 has a forward incompatible TASTy version 28.4,
+      """Forward incompatible TASTy file has version 28.4, produced by Scala 3.4.2,
         |  expected stable TASTy from 28.0 to 28.3, or exactly 28.4-experimental-1.
         |  To read this TASTy file, use a Scala 3.4.0 compiler or newer.
         |  Please refer to the documentation for information on TASTy versioning:
@@ -238,7 +238,7 @@ class TastyHeaderUnpicklerTest {
     val file = TastyVersion(28, 4, 2)
     val read = TastyVersion(28, 4, 1)
     expectUnpickleError(runTest(file, read, "Scala 3.3.3-RC2-NIGHTLY")) {
-      """TASTy file produced by Scala 3.3.3-RC2-NIGHTLY has a forward incompatible TASTy version 28.4-experimental-2,
+      """Forward incompatible TASTy file has version 28.4-experimental-2, produced by Scala 3.3.3-RC2-NIGHTLY,
         |  expected stable TASTy from 28.0 to 28.3, or exactly 28.4-experimental-1.
         |  To read this experimental TASTy file, use the same nightly or snapshot Scala 3.3 compiler.
         |  Please refer to the documentation for information on TASTy versioning:
@@ -252,7 +252,7 @@ class TastyHeaderUnpicklerTest {
     val file = TastyVersion(28, 4, 2)
     val read = TastyVersion(28, 4, 1)
     expectUnpickleError(runTest(file, read, "Scala 3.3.3-RC2-NIGHTLY", generic = true)) {
-      """TASTy file produced by Scala 3.3.3-RC2-NIGHTLY has a forward incompatible TASTy version 28.4-experimental-2,
+      """Forward incompatible TASTy file has version 28.4-experimental-2, produced by Scala 3.3.3-RC2-NIGHTLY,
         |  expected stable TASTy from 28.0 to 28.3, or exactly 28.4-experimental-1.
         |  To read this experimental TASTy file, use the version of this tool compatible with TASTy 28.4-experimental-2.
         |  Please refer to the documentation for information on TASTy versioning:
diff --git a/tasty/src/dotty/tools/tasty/TastyHeaderUnpickler.scala b/tasty/src/dotty/tools/tasty/TastyHeaderUnpickler.scala
index 1a67913e68ca..db07666d3be1 100644
--- a/tasty/src/dotty/tools/tasty/TastyHeaderUnpickler.scala
+++ b/tasty/src/dotty/tools/tasty/TastyHeaderUnpickler.scala
@@ -103,7 +103,7 @@ class TastyHeaderUnpickler(config: UnpicklerConfig, reader: TastyReader) {
       val fileMinor = readNat()
       val fileVersion = TastyVersion(fileMajor, fileMinor, 0)
       val toolVersion = TastyVersion(toolMajor, toolMinor, toolExperimental)
-      val signature = signatureString(fileVersion, toolVersion, what = "backward", tool = None)
+      val signature = signatureString(fileVersion, toolVersion, what = "Backward", tool = None)
       val fix = recompileFix(toolVersion.minStable)
       throw new UnpickleException(signature + fix + tastyAddendum)
     }
@@ -141,7 +141,7 @@ class TastyHeaderUnpickler(config: UnpicklerConfig, reader: TastyReader) {
 
         val compat = Compatibility.failReason(file = fileVersion, read = toolVersion)
 
-        val what = if (compat < 0) "backward" else "forward"
+        val what = if (compat < 0) "Backward" else "Forward"
         val signature = signatureString(fileVersion, toolVersion, what, tool = Some(toolingVersion))
         val fix = (
           if (compat < 0) {
@@ -169,8 +169,8 @@ class TastyHeaderUnpickler(config: UnpicklerConfig, reader: TastyReader) {
 
   private def signatureString(
       fileVersion: TastyVersion, toolVersion: TastyVersion, what: String, tool: Option[String]) = {
-    val optProducedBy = tool.fold("")(t => s" produced by $t")
-    s"""TASTy file$optProducedBy has a $what incompatible TASTy version ${fileVersion.show},
+    val optProducedBy = tool.fold("")(t => s", produced by $t")
+    s"""$what incompatible TASTy file has version ${fileVersion.show}$optProducedBy,
       |  expected ${toolVersion.validRange}.
       |""".stripMargin
   }