diff --git a/lib/datadog/appsec/processor.rb b/lib/datadog/appsec/processor.rb
index ceebbfa8d81..e439e625e9e 100644
--- a/lib/datadog/appsec/processor.rb
+++ b/lib/datadog/appsec/processor.rb
@@ -14,9 +14,12 @@ def initialize(processor)
           @time_ext_ns = 0.0
           @timeouts = 0
           @events = []
+          @run_mutex = Mutex.new
         end
 
         def run(input, timeout = WAF::LibDDWAF::DDWAF_RUN_TIMEOUT)
+          @run_mutex.lock
+
           start_ns = Core::Utils::Time.get_time(:nanosecond)
 
           # TODO: remove multiple assignment
@@ -30,6 +33,8 @@ def run(input, timeout = WAF::LibDDWAF::DDWAF_RUN_TIMEOUT)
           @timeouts += 1 if res.timeout
 
           res
+        ensure
+          @run_mutex.unlock
         end
 
         def finalize
diff --git a/sig/datadog/appsec/processor.rbs b/sig/datadog/appsec/processor.rbs
index 94cecee5733..2e5e281bcb3 100644
--- a/sig/datadog/appsec/processor.rbs
+++ b/sig/datadog/appsec/processor.rbs
@@ -12,6 +12,8 @@ module Datadog
 
         @context: WAF::Context
 
+        @run_mutex: ::Thread::Mutex
+
         def initialize: (Processor processor) -> void
         def run: (data input, ?::Integer timeout) -> WAF::Result
         def finalize: () -> void