diff --git a/otafault/ota_io.cpp b/otafault/ota_io.cpp
index f5b0113..3a89bb5 100644
--- a/otafault/ota_io.cpp
+++ b/otafault/ota_io.cpp
@@ -89,7 +89,7 @@
     return fclose(fh);
 }
 
-void OtaFcloser::operator()(FILE* f) {
+void OtaFcloser::operator()(FILE* f) const {
     __ota_fclose(f);
 };
 
diff --git a/otafault/ota_io.h b/otafault/ota_io.h
index 395b423..9428f1b 100644
--- a/otafault/ota_io.h
+++ b/otafault/ota_io.h
@@ -59,7 +59,7 @@
 int ota_close(unique_fd& fd);
 
 struct OtaFcloser {
-  void operator()(FILE*);
+  void operator()(FILE*) const;
 };
 
 using unique_file = std::unique_ptr<FILE, OtaFcloser>;
diff --git a/screen_ui.cpp b/screen_ui.cpp
index 706877b..bb2772d 100644
--- a/screen_ui.cpp
+++ b/screen_ui.cpp
@@ -98,7 +98,7 @@
     }
 }
 
-int ScreenRecoveryUI::PixelsFromDp(int dp) {
+int ScreenRecoveryUI::PixelsFromDp(int dp) const {
     return dp * density_;
 }
 
@@ -256,12 +256,12 @@
     *y += 4;
 }
 
-void ScreenRecoveryUI::DrawTextLine(int x, int* y, const char* line, bool bold) {
+void ScreenRecoveryUI::DrawTextLine(int x, int* y, const char* line, bool bold) const {
     gr_text(gr_sys_font(), x, *y, line, bold);
     *y += char_height_ + 4;
 }
 
-void ScreenRecoveryUI::DrawTextLines(int x, int* y, const char* const* lines) {
+void ScreenRecoveryUI::DrawTextLines(int x, int* y, const char* const* lines) const {
     for (size_t i = 0; lines != nullptr && lines[i] != nullptr; ++i) {
         DrawTextLine(x, y, lines[i], false);
     }
diff --git a/screen_ui.h b/screen_ui.h
index b2dcf4a..a2322c3 100644
--- a/screen_ui.h
+++ b/screen_ui.h
@@ -160,14 +160,14 @@
     void LoadBitmap(const char* filename, GRSurface** surface);
     void LoadLocalizedBitmap(const char* filename, GRSurface** surface);
 
-    int PixelsFromDp(int dp);
+    int PixelsFromDp(int dp) const;
     virtual int GetAnimationBaseline();
     virtual int GetProgressBaseline();
     virtual int GetTextBaseline();
 
     void DrawHorizontalRule(int* y);
-    void DrawTextLine(int x, int* y, const char* line, bool bold);
-    void DrawTextLines(int x, int* y, const char* const* lines);
+    void DrawTextLine(int x, int* y, const char* line, bool bold) const;
+    void DrawTextLines(int x, int* y, const char* const* lines) const;
 };
 
 #endif  // RECOVERY_UI_H
diff --git a/verifier.cpp b/verifier.cpp
index e9d540c..23142c1 100644
--- a/verifier.cpp
+++ b/verifier.cpp
@@ -370,7 +370,7 @@
 }
 
 struct BNDeleter {
-  void operator()(BIGNUM* bn) {
+  void operator()(BIGNUM* bn) const {
     BN_free(bn);
   }
 };
diff --git a/verifier.h b/verifier.h
index 6bee749..6fa8f2b 100644
--- a/verifier.h
+++ b/verifier.h
@@ -26,13 +26,13 @@
 #include <openssl/sha.h>
 
 struct RSADeleter {
-  void operator()(RSA* rsa) {
+  void operator()(RSA* rsa) const {
     RSA_free(rsa);
   }
 };
 
 struct ECKEYDeleter {
-  void operator()(EC_KEY* ec_key) {
+  void operator()(EC_KEY* ec_key) const {
     EC_KEY_free(ec_key);
   }
 };