diff --git a/src/operator/ConcatImpl.cpp b/src/operator/ConcatImpl.cpp
index ceefb9031f279be417a8ab0485567a56edea7824..e142b79a8aad5a99a65fdf38de630f3b5668c804 100644
--- a/src/operator/ConcatImpl.cpp
+++ b/src/operator/ConcatImpl.cpp
@@ -87,4 +87,4 @@ void  Aidge::ConcatImpl_cpu::forward() {
                getCPUPtr(mOp.getRawOutput(0)));
 }
 
-void  Aidge::ConcatImpl_cpu::backward() { printf("Not implemented yet.\n"); }
\ No newline at end of file
+void  Aidge::ConcatImpl_cpu::backward() { fmt::print("Not implemented yet.\n"); }
\ No newline at end of file
diff --git a/src/operator/SliceImpl.cpp b/src/operator/SliceImpl.cpp
index 32d31f046465425a269d6f8e3fc52eaad31c663a..c1a6480c1e7c0d681abef12f06a57e140d1e9efd 100644
--- a/src/operator/SliceImpl.cpp
+++ b/src/operator/SliceImpl.cpp
@@ -79,4 +79,4 @@ void Aidge::SliceImpl_cpu::forward() {
     mNbProducedData[0] += getRequiredMemory(0, {});
 }
 
-void Aidge::SliceImpl_cpu::backward() { printf("Not implemented yet.\n"); }
+void Aidge::SliceImpl_cpu::backward() { fmt::print("Not implemented yet.\n"); }