diff --git a/src/ai/api/ai_error.cpp b/src/ai/api/ai_error.cpp
new file mode 100644
--- /dev/null
+++ b/src/ai/api/ai_error.cpp
@@ -0,0 +1,60 @@
+/* $Id$ */
+
+/** @file ai_error.cpp Implementation of AIError. */
+
+#include "ai_error.hpp"
+#include "table/strings.h"
+#include "../../core/bitmath_func.hpp"
+
+AIError::AIErrorMap AIError::error_map = AIError::AIErrorMap();
+AIError::AIErrorMapString AIError::error_map_string = AIError::AIErrorMapString();
+
+/* static */ AIErrorType AIError::GetLastError()
+{
+	return AIObject::GetLastError();
+}
+
+/* static */ const char *AIError::GetLastErrorString()
+{
+	return (*error_map_string.find(AIError::GetLastError())).second;
+}
+
+/* static */ AIErrorType AIError::StringToError(StringID internal_string_id)
+{
+	uint index = GB(internal_string_id, 11, 5);
+	switch (GB(internal_string_id, 11, 5)) {
+		case 26: case 28: case 29: case 30: // NewGRF strings.
+			return ERR_NEWGRF_SUPPLIED_ERROR;
+
+		/* DO NOT SWAP case 14 and 4 because that will break StringToError due
+		 * to the index dependency that relies on FALL THROUGHs. */
+		case 14: if (index < 0xE4) break; // Player name
+		case 4:  if (index < 0xC0) break; // Town name
+		case 15: // Custom name
+		case 31: // Dynamic strings
+			/* These strings are 'random' and have no meaning.
+			 * They actually shouldn't even be returned as error messages. */
+			return ERR_UNKNOWN;
+
+		default:
+			break;
+	}
+
+	AIErrorMap::iterator it = error_map.find(internal_string_id);
+	if (it == error_map.end()) return ERR_UNKNOWN;
+	return (*it).second;
+}
+
+/* static */ void AIError::RegisterErrorMap(StringID internal_string_id, AIErrorType ai_error_msg)
+{
+	error_map[internal_string_id] = ai_error_msg;
+}
+
+/* static */ void AIError::RegisterErrorMapString(AIErrorType ai_error_msg, const char *message)
+{
+	error_map_string[ai_error_msg] = message;
+}
+
+/* static */ AIError::ErrorCategories AIError::GetErrorCategory() {
+	return (AIError::ErrorCategories)(GetLastError() >> (uint)ERR_CAT_BIT_SIZE);
+}