diff --git a/CHANGELOG.md b/CHANGELOG.md
index b779f2e51..3d5353d22 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Proving of validity of message field after update with valid sequence (eng/recordflux/RecordFlux#1444)
+- User defined `GNATCOLL_ICONV_OPT` environment variable is ignored in Makefile (AdaCore/RecordFlux#1292, eng/recordflux/RecordFlux#1453)
 
 ## [0.15.0] - 2023-11-08
 
diff --git a/Makefile b/Makefile
index 7eb40b8b3..07bb04a73 100644
--- a/Makefile
+++ b/Makefile
@@ -320,7 +320,7 @@ parser: $(GENERATED_DIR)/python/librflxlang/librflxlang.so
 
 $(GENERATED_DIR)/python/librflxlang/librflxlang.so: export GPR_PROJECT_PATH := \
 	$(GPR_PROJECT_PATH):$(GENERATED_DIR)/langkit/langkit/support:$(GENERATED_DIR)/gnatcoll-bindings/gmp:$(GENERATED_DIR)/gnatcoll-bindings/iconv:$(GENERATED_DIR)/adasat
-$(GENERATED_DIR)/python/librflxlang/librflxlang.so: export GNATCOLL_ICONV_OPT := -v
+$(GENERATED_DIR)/python/librflxlang/librflxlang.so: export GNATCOLL_ICONV_OPT ?= -v
 $(GENERATED_DIR)/python/librflxlang/librflxlang.so: $(wildcard language/*.py) | $(GENERATED_DIR)/python/librflxlang
 	gprbuild -p -j0 -P$(GENERATED_DIR)/librflxlang.gpr \
 		-XLIBRARY_TYPE=static-pic \