diff --git a/src/lib/pbkdf/pwdhash.h b/src/lib/pbkdf/pwdhash.h
index 3065408ab96..4ca467864d2 100644
--- a/src/lib/pbkdf/pwdhash.h
+++ b/src/lib/pbkdf/pwdhash.h
@@ -78,7 +78,7 @@ class BOTAN_PUBLIC_API(2, 8) PasswordHash {
       * This function is const, but is not thread safe. Different threads should
       * either use unique objects, or serialize all access.
       */
-      void hash(std::span<uint8_t> out, std::string_view password, std::span<const uint8_t> salt) {
+      void hash(std::span<uint8_t> out, std::string_view password, std::span<const uint8_t> salt) const {
          this->derive_key(out.data(), out.size(), password.data(), password.size(), salt.data(), salt.size());
       }
 
@@ -98,7 +98,7 @@ class BOTAN_PUBLIC_API(2, 8) PasswordHash {
                 std::string_view password,
                 std::span<const uint8_t> salt,
                 std::span<const uint8_t> associated_data,
-                std::span<const uint8_t> key) {
+                std::span<const uint8_t> key) const {
          this->derive_key(out.data(),
                           out.size(),
                           password.data(),
diff --git a/src/lib/tls/tls_extensions.h b/src/lib/tls/tls_extensions.h
index 933daddd986..5577c237d90 100644
--- a/src/lib/tls/tls_extensions.h
+++ b/src/lib/tls/tls_extensions.h
@@ -282,7 +282,7 @@ class BOTAN_UNSTABLE_API Supported_Point_Formats final : public Extension {
 
       bool empty() const override { return false; }
 
-      bool prefers_compressed() { return m_prefers_compressed; }
+      bool prefers_compressed() const { return m_prefers_compressed; }
 
    private:
       bool m_prefers_compressed = false;
diff --git a/src/lib/utils/http_util/http_util.h b/src/lib/utils/http_util/http_util.h
index 58c1a666325..ad5aa9bf386 100644
--- a/src/lib/utils/http_util/http_util.h
+++ b/src/lib/utils/http_util/http_util.h
@@ -46,7 +46,7 @@ class Response final {
 
       std::string status_message() const { return m_status_message; }
 
-      void throw_unless_ok() {
+      void throw_unless_ok() const {
          if(status_code() != 200) {
             throw HTTP_Error(status_message());
          }
diff --git a/src/lib/utils/timer.h b/src/lib/utils/timer.h
index 2c1d60017ca..d317810d4b4 100644
--- a/src/lib/utils/timer.h
+++ b/src/lib/utils/timer.h
@@ -34,7 +34,7 @@ class BOTAN_TEST_API Timer final {
 
       void stop();
 
-      bool under(std::chrono::milliseconds msec) { return (milliseconds() < msec.count()); }
+      bool under(std::chrono::milliseconds msec) const { return (milliseconds() < msec.count()); }
 
       class Timer_Scope final {
          public: