diff --git a/CMakeLists.txt b/CMakeLists.txt
index 711287f48..001574af7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -430,6 +430,7 @@ if (LLAMA_ALL_WARNINGS)
             -Wpointer-arith
             -Wmissing-prototypes
             -Werror=implicit-int
+            -Werror=implicit-function-declaration
         )
         set(cxx_flags
             ${warning_flags}
diff --git a/Makefile b/Makefile
index 3dd93d015..8118ea489 100644
--- a/Makefile
+++ b/Makefile
@@ -175,7 +175,7 @@ endif # LLAMA_DISABLE_LOGS
 # warnings
 WARN_FLAGS    = -Wall -Wextra -Wpedantic -Wcast-qual -Wno-unused-function
 MK_CFLAGS    += $(WARN_FLAGS) -Wdouble-promotion -Wshadow -Wstrict-prototypes -Wpointer-arith -Wmissing-prototypes \
-				-Werror=implicit-int
+				-Werror=implicit-int -Werror=implicit-function-declaration
 MK_CXXFLAGS  += $(WARN_FLAGS) -Wmissing-declarations -Wmissing-noreturn -Wextra-semi
 
 # TODO(cebtenzzre): remove this once PR #2632 gets merged