diff --git a/README.md b/README.md
index 3678cad..337a650 100644
--- a/README.md
+++ b/README.md
@@ -77,8 +77,8 @@ make check-stress   # randomized, capacity, collision, failure, and restart test
 tests. `make docker-check` force-rebuilds and runs all three tiers in the
 container; run `make docker-image` first after changing `Dockerfile`.
 
-Native Linux builds require a C toolchain, Make, pkg-config, Python 3, and
-cmp/diff, plus:
+Native Linux source builds require a C toolchain, Make, pkg-config, Python 3,
+and cmp/diff, plus development files for:
 
 - Plan 9 port (`9c`, `9l`, `libthread`, and `libbio`);
 - D-Bus development files;
@@ -133,10 +133,17 @@ export GTK_IM_MODULE=strans
 GLFW_IM_MODULE=ibus kitty
 ```
 
-The GTK module directory is derived from GTK's pkg-config `libdir` and binary
-version. It can be overridden with `GTK_MODULE_DIR`; `DESTDIR` staging is
-supported and deliberately skips the host module-cache update. Remove a
-native installation with:
+Building `gtk/im-strans.so` requires GTK development files. Installing an
+already-built, up-to-date module from this build tree does not: the install
+target first uses an explicit `GTK_MODULE_DIR`, then GTK's pkg-config
+variables, and finally the module directory reported by the GTK runtime's
+`gtk-query-immodules-3.0`. Packagers and cross builds should set
+`GTK_MODULE_DIR` explicitly. A prebuilt module must still match the target
+architecture and library ABI.
+
+`DESTDIR` staging is supported and deliberately skips the host module-cache
+update. A native install needs the GTK runtime query utility so it can refresh
+that cache. Remove a native installation with:
 
 ```sh
 doas make -C gtk uninstall
diff --git a/gtk/Makefile b/gtk/Makefile
index b1283bc..98f4a6a 100644
--- a/gtk/Makefile
+++ b/gtk/Makefile
@@ -3,10 +3,17 @@ PKG_CONFIG ?= pkg-config
 CFLAGS ?= -O2
 GTK_CFLAGS = $(shell $(PKG_CONFIG) --cflags gtk+-3.0)
 GTK_LIBS = $(shell $(PKG_CONFIG) --libs gtk+-3.0)
-GTK_LIBDIR ?= $(shell $(PKG_CONFIG) --variable=libdir gtk+-3.0)
-GTK_BINARY_VERSION ?= $(shell $(PKG_CONFIG) --variable=gtk_binary_version gtk+-3.0)
-GTK_MODULE_DIR ?= $(GTK_LIBDIR)/gtk-3.0/$(GTK_BINARY_VERSION)/immodules
 GTK_QUERY_IMMODULES ?= gtk-query-immodules-3.0
+GTK_LIBDIR ?= $(shell $(PKG_CONFIG) --variable=libdir gtk+-3.0 2>/dev/null)
+GTK_BINARY_VERSION ?= $(shell $(PKG_CONFIG) \
+	--variable=gtk_binary_version gtk+-3.0 2>/dev/null)
+GTK_RUNTIME_MODULE_DIR = $(shell GTK_PATH= GTK_IM_MODULE_FILE= \
+	$(GTK_QUERY_IMMODULES) 2>/dev/null | \
+	awk -F '"' '/^"\// { sub("/[^/]*$$", "", $$2); print $$2; exit }')
+GTK_MODULE_DIR ?= $(strip $(if \
+	$(and $(strip $(GTK_LIBDIR)),$(strip $(GTK_BINARY_VERSION))),\
+	$(GTK_LIBDIR)/gtk-3.0/$(GTK_BINARY_VERSION)/immodules,\
+	$(GTK_RUNTIME_MODULE_DIR)))
 
 all: $(PROG)
 
@@ -15,19 +22,29 @@ $(PROG): main.c ../ipc.c ../ipc.h
 		-shared -fPIC -o $@ main.c ../ipc.c $(GTK_LIBS) $(LDLIBS)
 
 install: $(PROG)
-	test -n "$(GTK_LIBDIR)"
-	test -n "$(GTK_BINARY_VERSION)"
-	test -n "$(GTK_MODULE_DIR)"
-	mkdir -p "$(DESTDIR)$(GTK_MODULE_DIR)"
-	cp $(PROG) "$(DESTDIR)$(GTK_MODULE_DIR)/"
-	if test -z "$(DESTDIR)"; then $(GTK_QUERY_IMMODULES) --update-cache; fi
+	module_dir="$(GTK_MODULE_DIR)"; \
+	test -n "$$module_dir" || { \
+		echo "cannot find GTK 3 module directory; set GTK_MODULE_DIR" >&2; \
+		exit 1; \
+	}; \
+	mkdir -p "$(DESTDIR)$$module_dir" && \
+	cp "$(PROG)" "$(DESTDIR)$$module_dir/" && \
+	if test -z "$(DESTDIR)"; then \
+		GTK_PATH= GTK_IM_MODULE_FILE= \
+		$(GTK_QUERY_IMMODULES) --update-cache; \
+	fi
 
 uninstall:
-	test -n "$(GTK_LIBDIR)"
-	test -n "$(GTK_BINARY_VERSION)"
-	test -n "$(GTK_MODULE_DIR)"
-	rm -f "$(DESTDIR)$(GTK_MODULE_DIR)/$(PROG)"
-	if test -z "$(DESTDIR)"; then $(GTK_QUERY_IMMODULES) --update-cache; fi
+	module_dir="$(GTK_MODULE_DIR)"; \
+	test -n "$$module_dir" || { \
+		echo "cannot find GTK 3 module directory; set GTK_MODULE_DIR" >&2; \
+		exit 1; \
+	}; \
+	rm -f "$(DESTDIR)$$module_dir/$(PROG)" && \
+	if test -z "$(DESTDIR)"; then \
+		GTK_PATH= GTK_IM_MODULE_FILE= \
+		$(GTK_QUERY_IMMODULES) --update-cache; \
+	fi
 
 clean:
 	rm -f $(PROG)