diff --git a/src/secp256k1/CMakeLists.txt b/src/secp256k1/CMakeLists.txt
--- a/src/secp256k1/CMakeLists.txt
+++ b/src/secp256k1/CMakeLists.txt
@@ -76,7 +76,7 @@
 # For convenience, we wrap this into a function.
 function(link_secp256k1_internal NAME)
 	target_link_libraries(${NAME} secp256k1)
-	target_compile_definitions(${NAME} PRIVATE HAVE_CONFIG_H)
+	target_compile_definitions(${NAME} PRIVATE HAVE_CONFIG_H SECP256K1_BUILD)
 endfunction(link_secp256k1_internal)
 
 # Phony target to build benchmarks
@@ -127,7 +127,7 @@
 
 # Generate the config
 configure_file(src/libsecp256k1-config.h.cmake.in src/libsecp256k1-config.h ESCAPE_QUOTES)
-target_compile_definitions(secp256k1 PRIVATE HAVE_CONFIG_H)
+target_compile_definitions(secp256k1 PRIVATE HAVE_CONFIG_H SECP256K1_BUILD)
 
 # Tests
 option(SECP256K1_BUILD_TEST "Build secp256k1's unit tests" ON)