diff --git a/src/util/strencodings.cpp b/src/util/strencodings.cpp
index a54f408496b..6fc6c30bb40 100644
--- a/src/util/strencodings.cpp
+++ b/src/util/strencodings.cpp
@@ -444,6 +444,7 @@ bool ParseFixedPoint(std::string_view val, int decimals, int64_t *amount_out)
 std::string ToLower(std::string_view str)
 {
     std::string r;
+    r.reserve(str.size());
     for (auto ch : str) r += ToLower(ch);
     return r;
 }
@@ -451,6 +452,7 @@ std::string ToLower(std::string_view str)
 std::string ToUpper(std::string_view str)
 {
     std::string r;
+    r.reserve(str.size());
     for (auto ch : str) r += ToUpper(ch);
     return r;
 }