diff --git a/.github/workflows/regex-engine.yml b/.github/workflows/regex-engine.yml
index c75093d01378..ac3ac7c52fb0 100644
--- a/.github/workflows/regex-engine.yml
+++ b/.github/workflows/regex-engine.yml
@@ -24,8 +24,8 @@ jobs:
       - name: Install PCRE2
         run: apk add pcre2-dev
       - name: Assert using PCRE2
-        run: bin/crystal eval -Duse_pcre2 'abort unless Regex::Engine == Regex::PCRE2'
+        run: bin/crystal eval 'abort unless Regex::Engine == Regex::PCRE2'
       - name: Assert select PCRE
         run: bin/crystal eval -Duse_pcre 'abort unless Regex::Engine == Regex::PCRE'
       - name: Run Regex specs
-        run: bin/crystal spec -Duse_pcre2 --order=random spec/std/regex*
+        run: bin/crystal spec --order=random spec/std/regex*
diff --git a/.github/workflows/win.yml b/.github/workflows/win.yml
index e06a0ef88f03..8957e98963f2 100644
--- a/.github/workflows/win.yml
+++ b/.github/workflows/win.yml
@@ -15,7 +15,7 @@ jobs:
           make deps
       - name: Cross-compile Crystal
         run: |
-          LLVM_TARGETS=X86 bin/crystal build --cross-compile --target x86_64-pc-windows-msvc src/compiler/crystal.cr -Dwithout_playground -Dwithout_iconv -Dwithout_interpreter
+          LLVM_TARGETS=X86 bin/crystal build --cross-compile --target x86_64-pc-windows-msvc src/compiler/crystal.cr -Dwithout_playground -Dwithout_iconv -Dwithout_interpreter -Duse_pcre
 
       - name: Upload Crystal object file
         uses: actions/upload-artifact@v3
diff --git a/Makefile b/Makefile
index 7db99f0be775..7eadaf4e9f3d 100644
--- a/Makefile
+++ b/Makefile
@@ -197,7 +197,7 @@ $(O)/primitives_spec: $(O)/crystal $(DEPS) $(SOURCES) $(SPEC_SOURCES)
 $(O)/crystal: $(DEPS) $(SOURCES)
 	$(call check_llvm_config)
 	@mkdir -p $(O)
-	$(EXPORTS) $(EXPORTS_BUILD) ./bin/crystal build $(FLAGS) -o $@ src/compiler/crystal.cr -D without_openssl -D without_zlib
+	$(EXPORTS) $(EXPORTS_BUILD) ./bin/crystal build $(FLAGS) -o $@ src/compiler/crystal.cr -D without_openssl -D without_zlib -D use_pcre
 
 $(LLVM_EXT_OBJ): $(LLVM_EXT_DIR)/llvm_ext.cc
 	$(call check_llvm_config)
diff --git a/Makefile.win b/Makefile.win
index 7c10931ef1d3..dc89bcc74a8c 100644
--- a/Makefile.win
+++ b/Makefile.win
@@ -190,7 +190,7 @@ $(O)\crystal.exe: $(DEPS) $(SOURCES) $(O)\crystal.res
 	@$(call MKDIR,"$(O)")
 	$(call export_vars)
 	$(call export_build_vars)
-	.\bin\crystal build $(FLAGS) -o "$(O)\crystal-next.exe" src\compiler\crystal.cr -D without_openssl -D without_zlib -D without_playground --link-flags=/PDBALTPATH:crystal.pdb "--link-flags=$(realpath $(O)\crystal.res)"
+	.\bin\crystal build $(FLAGS) -o "$(O)\crystal-next.exe" src\compiler\crystal.cr -D without_openssl -D without_zlib -D without_playground -D use_pcre --link-flags=/PDBALTPATH:crystal.pdb "--link-flags=$(realpath $(O)\crystal.res)"
 	$(call MV,"$(O)\crystal-next.exe","$@")
 	$(call MV,"$(O)\crystal-next.pdb","$(O)\crystal.pdb")
 
diff --git a/src/regex/engine.cr b/src/regex/engine.cr
index c2a336accd0d..6c0fdc2e6217 100644
--- a/src/regex/engine.cr
+++ b/src/regex/engine.cr
@@ -1,4 +1,8 @@
-{% if flag?(:use_pcre2) %}
+# The following condition ensures that the engine selection respects `-Duse_pcre2`/`-Duse_pcre`,
+# and if none is given it tries to check for availability of `libpcre2` with `pkg-config`.
+# If `pkg-config` is unavailable, the default is PCRE2. If `pkg-config` is available but
+# has no information about a `libpcre2` package, it falls back to PCRE.
+{% if flag?(:use_pcre2) || (!flag?(:use_pcre) && (flag?(:win32) || `hash pkg-config 2> /dev/null && (pkg-config --silence-errors --modversion libpcre2-8 || printf %s false) || true` != "false")) %}
   require "./pcre2"
 
   # :nodoc: