diff --git a/CHANGELOG.md b/CHANGELOG.md
index 315b777de..4652485d1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,9 @@
 - Update Kotlin to 1.6.20
 - Publish JS target with the IR format in addition to LEGACY
 
+### Fixed
+- Fix race condition when using ProgressAnimation and adding interceptors in JVM [(#55)](https://github.com/ajalt/mordant/issues/55)
+
 # 2.0.0-beta5
 ### Added
 - Progress bars and other single-line animations are now supported in the IntelliJ console [(#49)](https://github.com/ajalt/mordant/issues/49)
diff --git a/mordant/src/commonMain/kotlin/com/github/ajalt/mordant/internal/MppH.kt b/mordant/src/commonMain/kotlin/com/github/ajalt/mordant/internal/MppH.kt
index 1133cd575..b7f62637d 100644
--- a/mordant/src/commonMain/kotlin/com/github/ajalt/mordant/internal/MppH.kt
+++ b/mordant/src/commonMain/kotlin/com/github/ajalt/mordant/internal/MppH.kt
@@ -38,5 +38,6 @@ internal expect fun sendInterceptedPrintRequest(
     request: PrintRequest,
     terminalInterface: TerminalInterface,
     interceptors: List<TerminalInterceptor>,
-    lock: Any,
 )
+
+internal expect inline fun synchronizeJvm(lock: Any, block: () -> Unit)
diff --git a/mordant/src/commonMain/kotlin/com/github/ajalt/mordant/terminal/Terminal.kt b/mordant/src/commonMain/kotlin/com/github/ajalt/mordant/terminal/Terminal.kt
index c64e4b905..2177b96ad 100644
--- a/mordant/src/commonMain/kotlin/com/github/ajalt/mordant/terminal/Terminal.kt
+++ b/mordant/src/commonMain/kotlin/com/github/ajalt/mordant/terminal/Terminal.kt
@@ -3,6 +3,7 @@ package com.github.ajalt.mordant.terminal
 import com.github.ajalt.mordant.internal.makePrintingTerminalCursor
 import com.github.ajalt.mordant.internal.renderLinesAnsi
 import com.github.ajalt.mordant.internal.sendInterceptedPrintRequest
+import com.github.ajalt.mordant.internal.synchronizeJvm
 import com.github.ajalt.mordant.rendering.*
 import com.github.ajalt.mordant.table.table
 import com.github.ajalt.mordant.widgets.HorizontalRule
@@ -250,11 +251,15 @@ class Terminal(
     }
 
     internal fun addInterceptor(interceptor: TerminalInterceptor) {
-        interceptors += interceptor
+        synchronizeJvm(lock) {
+            interceptors += interceptor
+        }
     }
 
     internal fun removeInterceptor(interceptor: TerminalInterceptor) {
-        interceptors.remove(interceptor)
+        synchronizeJvm(lock) {
+            interceptors.remove(interceptor)
+        }
     }
 
     private fun rawPrintln(message: String) {
@@ -266,6 +271,8 @@ class Terminal(
     }
 
     private fun sendPrintRequest(request: PrintRequest) {
-        sendInterceptedPrintRequest(request, terminalInterface, interceptors, lock)
+        synchronizeJvm(lock) {
+            sendInterceptedPrintRequest(request, terminalInterface, interceptors)
+        }
     }
 }
diff --git a/mordant/src/jsMain/kotlin/com/github/ajalt/mordant/internal/MppImpl.kt b/mordant/src/jsMain/kotlin/com/github/ajalt/mordant/internal/MppImpl.kt
index 664f48ebe..f4c0b9152 100644
--- a/mordant/src/jsMain/kotlin/com/github/ajalt/mordant/internal/MppImpl.kt
+++ b/mordant/src/jsMain/kotlin/com/github/ajalt/mordant/internal/MppImpl.kt
@@ -115,9 +115,10 @@ internal actual fun sendInterceptedPrintRequest(
     request: PrintRequest,
     terminalInterface: TerminalInterface,
     interceptors: List<TerminalInterceptor>,
-    lock: Any,
 ) {
     terminalInterface.completePrintRequest(
         interceptors.fold(request) { acc, it -> it.intercept(acc) }
     )
 }
+
+internal actual inline fun synchronizeJvm(lock: Any, block: () -> Unit) = block()
diff --git a/mordant/src/jvmMain/kotlin/com/github/ajalt/mordant/internal/MppImpl.kt b/mordant/src/jvmMain/kotlin/com/github/ajalt/mordant/internal/MppImpl.kt
index 7a446a416..25c09107d 100644
--- a/mordant/src/jvmMain/kotlin/com/github/ajalt/mordant/internal/MppImpl.kt
+++ b/mordant/src/jvmMain/kotlin/com/github/ajalt/mordant/internal/MppImpl.kt
@@ -131,11 +131,10 @@ internal actual fun sendInterceptedPrintRequest(
     request: PrintRequest,
     terminalInterface: TerminalInterface,
     interceptors: List<TerminalInterceptor>,
-    lock: Any,
 ) {
-    synchronized(lock) {
-        terminalInterface.completePrintRequest(
-            interceptors.fold(request) { acc, it -> it.intercept(acc) }
-        )
-    }
+    terminalInterface.completePrintRequest(
+        interceptors.fold(request) { acc, it -> it.intercept(acc) }
+    )
 }
+
+internal actual inline fun synchronizeJvm(lock: Any, block: () -> Unit) = synchronized(lock, block)
diff --git a/mordant/src/nativeMain/kotlin/com/github/ajalt/mordant/internal/MppImpl.kt b/mordant/src/nativeMain/kotlin/com/github/ajalt/mordant/internal/MppImpl.kt
index d1c784e9b..ca9e787e3 100644
--- a/mordant/src/nativeMain/kotlin/com/github/ajalt/mordant/internal/MppImpl.kt
+++ b/mordant/src/nativeMain/kotlin/com/github/ajalt/mordant/internal/MppImpl.kt
@@ -110,9 +110,10 @@ internal actual fun sendInterceptedPrintRequest(
     request: PrintRequest,
     terminalInterface: TerminalInterface,
     interceptors: List<TerminalInterceptor>,
-    lock: Any,
 ) {
     terminalInterface.completePrintRequest(
         interceptors.fold(request) { acc, it -> it.intercept(acc) }
     )
 }
+
+internal actual inline fun synchronizeJvm(lock: Any, block: () -> Unit) = block()