diff --git a/src/ai/ai_config.cpp b/src/ai/ai_config.cpp
index c3c9a5c205..2afa69d39e 100644
--- a/src/ai/ai_config.cpp
+++ b/src/ai/ai_config.cpp
@@ -125,3 +125,14 @@ void AIConfig::SetSetting(const char *name, int value)
 
 	ScriptConfig::SetSetting(name, value);
 }
+
+void AIConfig::AddRandomDeviation()
+{
+	int start_date = this->GetSetting("start_date");
+
+	ScriptConfig::AddRandomDeviation();
+
+	/* start_date = 0 is a special case, where random deviation does not occur.
+	 * If start_date was not already 0, then a minimum value of 1 must apply. */
+	this->SetSetting("start_date", start_date != 0 ? max(1, this->GetSetting("start_date")) : 0);
+}
diff --git a/src/script/script_config.hpp b/src/script/script_config.hpp
index adadcd35c9..31004caba7 100644
--- a/src/script/script_config.hpp
+++ b/src/script/script_config.hpp
@@ -137,7 +137,7 @@ public:
 	/**
 	 * Randomize all settings the Script requested to be randomized.
 	 */
-	void AddRandomDeviation();
+	virtual void AddRandomDeviation();
 
 	/**
 	 * Is this config attached to an Script? In other words, is there a Script