diff --git a/src/config/Data.cxx b/src/config/Data.cxx
index f4535c599..6ab5f20ba 100644
--- a/src/config/Data.cxx
+++ b/src/config/Data.cxx
@@ -21,7 +21,7 @@
 #include "Data.hxx"
 #include "Param.hxx"
 #include "Block.hxx"
-#include "system/FatalError.hxx"
+#include "util/RuntimeError.hxx"
 #include "util/StringAPI.hxx"
 
 void
@@ -40,14 +40,14 @@ ConfigData::Clear()
 
 const ConfigBlock *
 ConfigData::FindBlock(ConfigBlockOption option,
-		      const char *key, const char *value) const noexcept
+		      const char *key, const char *value) const
 {
 	for (const auto *block = GetBlock(option);
 	     block != nullptr; block = block->next) {
 		const char *value2 = block->GetBlockValue(key);
 		if (value2 == nullptr)
-			FormatFatalError("block without '%s' in line %d",
-					 key, block->line);
+			throw FormatRuntimeError("block without '%s' in line %d",
+						 key, block->line);
 
 		if (StringIsEqual(value2, value))
 			return block;
diff --git a/src/config/Data.hxx b/src/config/Data.hxx
index 940440d7d..45ce1c95a 100644
--- a/src/config/Data.hxx
+++ b/src/config/Data.hxx
@@ -43,9 +43,12 @@ struct ConfigData {
 		return blocks[size_t(option)];
 	}
 
+	/**
+	 * Throws if a block doesn't have the specified (mandatory) key.
+	 */
 	gcc_pure
 	const ConfigBlock *FindBlock(ConfigBlockOption option,
-				     const char *key, const char *value) const noexcept;
+				     const char *key, const char *value) const;
 };
 
 #endif