diff --git a/repos/base/mk/dep_lib.mk b/repos/base/mk/dep_lib.mk
index c788b8ff64..0648a8c2db 100644
--- a/repos/base/mk/dep_lib.mk
+++ b/repos/base/mk/dep_lib.mk
@@ -119,8 +119,9 @@ warn_unsatisfied_requirements: generate_lib_rule_for_defect_library
 	@$(ECHO) "Skip library $(LIB) because it requires $(DARK_COL)$(UNSATISFIED_REQUIREMENTS)$(DEFAULT_COL)"
 
 generate_lib_rule_for_defect_library:
-	@echo "INVALID_DEPS += $(LIB)" >> $(LIB_DEP_FILE)
-	@echo "" >> $(LIB_DEP_FILE)
+	@(echo "INVALID_DEPS += $(LIB)"; \
+	  echo "$(LIB).lib:"; \
+	  echo "") >> $(LIB_DEP_FILE)
 
 LIBS_TO_VISIT = $(filter-out $(LIBS_READY),$(LIBS))
 
diff --git a/repos/base/src/lib/target.mk b/repos/base/src/lib/target.mk
deleted file mode 100644
index c7315d49ca..0000000000
--- a/repos/base/src/lib/target.mk
+++ /dev/null
@@ -1,33 +0,0 @@
-#
-# This is a dummy target description file with the sole purpose of building
-# all libraries.
-#
-TARGET = libs
-
-#
-# Determine all 'lib/mk' sub directories residing within the repositories.
-# Use 'wildcard' to handle the case when a repository does not host any
-# 'lib/mk' sub directory.
-#
-LIB_MK_DIRS := $(wildcard $(addsuffix /lib/mk,$(REPOSITORIES)))
-
-#
-# Scan the 'lib/mk' directories of all repositories for library description
-# files.
-#
-ALL_LIB_MK_FILES := $(notdir $(foreach DIR,$(LIB_MK_DIRS),$(shell find $(DIR) -name "*.mk")))
-
-#
-# Make the pseudo target depend on all libraries, for which an lib.mk file
-# exists. Discard the '.mk' suffix and remove duplicates (via 'sort').
-#
-LIBS = $(sort $(ALL_LIB_MK_FILES:.mk=))
-
-#
-# Among all libraries found above, there may be several libraries with
-# unsatisfied build requirements. Normally, the build system won't attempt to
-# build the target (and its library dependencies) if one or more libraries
-# cannot be built. By enabling 'FORCE_BUILD_LIBS', we let the build system
-# visit all non-invalid libraries even in the presence of invalid libraries.
-#
-FORCE_BUILD_LIBS = yes
diff --git a/tool/builddir/build.mk b/tool/builddir/build.mk
index a0fe37bae2..ed31c74654 100644
--- a/tool/builddir/build.mk
+++ b/tool/builddir/build.mk
@@ -154,12 +154,35 @@ export LIBGCC_INC_DIR := $(shell dirname `$(CUSTOM_CXX_LIB) -print-libgcc-file-n
 #
 # Find out about the target directories to build
 #
-DST_DIRS := $(filter-out clean cleanall again run/%,$(MAKECMDGOALS))
+# Arguments starting with 'run/' and 'lib/' are special. The former triggers
+# the execution of a run script. The latter issues the build of a library.
+#
+DST_DIRS := $(filter-out clean cleanall again run/% lib/%,$(MAKECMDGOALS))
 
 ifeq ($(MAKECMDGOALS),)
 DST_DIRS := *
 endif
 
+#
+# Detect use of obsoleted LIB=<libname> option
+#
+ifneq ($(LIB),)
+$(error the 'LIB=$(LIB)' option is no longer supported, use 'make lib/$(LIB)')
+endif
+
+#
+# Determine library targets specified as lib/<libname> at the command line
+#
+LIBS := $(notdir $(filter lib/%,$(MAKECMDGOALS)))
+
+ifeq ($(MAKECMDGOALS),)
+ALL_LIB_MK_DIRS  := $(wildcard \
+                       $(foreach R,$(REPOSITORIES),\
+                          $R/lib/mk $(foreach S,$(SPECS),$R/lib/mk/spec/$S)))
+ALL_LIB_MK_FILES := $(wildcard $(addsuffix /*.mk,$(ALL_LIB_MK_DIRS)))
+LIBS             := $(sort $(notdir $(ALL_LIB_MK_FILES:.mk=)))
+endif
+
 #
 # Helper function to check if a needed tool is installed
 #
@@ -187,7 +210,7 @@ endif
 #
 # Default rule: build all directories specified as make arguments
 #
-_all $(DST_DIRS): gen_deps_and_build_targets
+_all $(DST_DIRS) $(addprefix lib/,$(LIBS)) : gen_deps_and_build_targets
 	@true
 
 ##
@@ -275,8 +298,15 @@ endif
 # we would need to spawn one additional shell per target, which would take
 # 10-20 percent more time.
 #
-traverse_target_dependencies: $(dir $(LIB_DEP_FILE)) init_libdep_file init_progress_log
+traverse_dependencies: $(dir $(LIB_DEP_FILE)) init_libdep_file init_progress_log
 	$(VERBOSE_MK) \
+	for lib in $(LIBS); do \
+	    $(MAKE) $(VERBOSE_DIR) -f $(BASE_DIR)/mk/dep_lib.mk \
+	            REP_DIR=$$rep LIB=$$lib \
+	            BUILD_BASE_DIR=$(BUILD_BASE_DIR) \
+	            DARK_COL="$(DARK_COL)" DEFAULT_COL="$(DEFAULT_COL)"; \
+	    echo "all: $$lib.lib" >> $(LIB_DEP_FILE); \
+	done; \
 	for target in $(TARGETS_TO_VISIT); do \
 	  for rep in $(REPOSITORIES); do \
 	    test -f $$rep/src/$$target || continue; \
@@ -288,29 +318,9 @@ traverse_target_dependencies: $(dir $(LIB_DEP_FILE)) init_libdep_file init_progr
 	  done; \
 	done; $$result;
 
-#
-# Generate content of libdep file if manually building a single library
-# specified via the 'LIB' argument.
-#
-traverse_lib_dependencies: $(dir $(LIB_DEP_FILE)) init_libdep_file init_progress_log
-	$(VERBOSE_MK) \
-	$(MAKE) $(VERBOSE_DIR) -f $(BASE_DIR)/mk/dep_lib.mk \
-	        REP_DIR=$$rep LIB=$(LIB) \
-	        BUILD_BASE_DIR=$(BUILD_BASE_DIR) \
-	        DARK_COL="$(DARK_COL)" DEFAULT_COL="$(DEFAULT_COL)"; \
-	echo "all: $(LIB).lib" >> $(LIB_DEP_FILE); \
-
 .PHONY: $(LIB_DEP_FILE)
 
-#
-# Depending on whether the top-level target is a list of targets or a
-# single library, we populate the LIB_DEP_FILE differently.
-#
-ifeq ($(LIB),)
-$(LIB_DEP_FILE): traverse_target_dependencies
-else
-$(LIB_DEP_FILE): traverse_lib_dependencies
-endif
+$(LIB_DEP_FILE): traverse_dependencies
 
 
 ##
diff --git a/tool/run/boot_dir/okl4 b/tool/run/boot_dir/okl4
index 30d60f2620..fd430acafb 100644
--- a/tool/run/boot_dir/okl4
+++ b/tool/run/boot_dir/okl4
@@ -99,7 +99,7 @@ proc core_link_address { } { return "0x03000000" }
 
 
 proc elfweaver {} {
-	if { ![file exists tool/okl4/elfweaver] } { build LIB=tools }
+	if { ![file exists tool/okl4/elfweaver] } { build lib/tools }
 	return tool/okl4/elfweaver
 }