diff --git a/3rdparty/everest/CMakeLists.txt b/3rdparty/everest/CMakeLists.txt
index eefc151..e0e5ade 100644
--- a/3rdparty/everest/CMakeLists.txt
+++ b/3rdparty/everest/CMakeLists.txt
@@ -18,11 +18,11 @@
 # everest is not directly linked against any mbedtls targets
 # so does not inherit the compile definitions.
 if(MBEDTLS_CONFIG_FILE)
-    target_compile_definitions(everest
+    target_compile_definitions(${everest_target}
         PUBLIC MBEDTLS_CONFIG_FILE="${MBEDTLS_CONFIG_FILE}")
 endif()
 if(MBEDTLS_USER_CONFIG_FILE)
-    target_compile_definitions(everest
+    target_compile_definitions(${everest_target}
         PUBLIC MBEDTLS_USER_CONFIG_FILE="${MBEDTLS_USER_CONFIG_FILE}")
 endif()
 
diff --git a/3rdparty/p256-m/CMakeLists.txt b/3rdparty/p256-m/CMakeLists.txt
index 41be3c4..2ef0d48 100644
--- a/3rdparty/p256-m/CMakeLists.txt
+++ b/3rdparty/p256-m/CMakeLists.txt
@@ -16,11 +16,11 @@
 # p256m is not directly linked against any mbedtls targets
 # so does not inherit the compile definitions.
 if(MBEDTLS_CONFIG_FILE)
-    target_compile_definitions(p256m
+    target_compile_definitions(${p256m_target}
         PUBLIC MBEDTLS_CONFIG_FILE="${MBEDTLS_CONFIG_FILE}")
 endif()
 if(MBEDTLS_USER_CONFIG_FILE)
-    target_compile_definitions(p256m
+    target_compile_definitions(${p256m_target}
         PUBLIC MBEDTLS_USER_CONFIG_FILE="${MBEDTLS_USER_CONFIG_FILE}")
 endif()
 
diff --git a/ChangeLog.d/fix-3rdparty-target-prefix.txt b/ChangeLog.d/fix-3rdparty-target-prefix.txt
new file mode 100644
index 0000000..db8ed07
--- /dev/null
+++ b/ChangeLog.d/fix-3rdparty-target-prefix.txt
@@ -0,0 +1,3 @@
+Bugfix
+   * Fix accidental omission of MBEDTLS_TARGET_PREFIX in 3rdparty modules
+     in CMake.