diff --git a/.github/workflows/http3-linux.yml b/.github/workflows/http3-linux.yml
index 732ca11550..3f21c91507 100644
--- a/.github/workflows/http3-linux.yml
+++ b/.github/workflows/http3-linux.yml
@@ -346,6 +346,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 10
     env:
+      CURL_TRACE_PKG_CONFIG: '1'
       MATRIX_BUILD: ${{ matrix.build.generate && 'cmake' || 'autotools' }}
       MATRIX_INSTALL_PACKAGES: '${{ matrix.build.install_packages }}'
     strategy:
diff --git a/acinclude.m4 b/acinclude.m4
index 646074fb65..ed48a6eb3a 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -1326,6 +1326,29 @@ AC_DEFUN([CURL_EXPORT_PCDIR], [
   fi
 ])
 
+dnl CURL_TRACE_PCDIR ($module, [$pcdir])
+dnl ------------------------
+dnl show pkg-config module lookup details, along with a detailed errors
+dnl message in case of failure. Supports both pkg-config and pkgconf.
+dnl
+
+AC_DEFUN([CURL_TRACE_PCDIR], [
+  dnl Example pkgconf line:
+  dnl   libpkgconf/pkg.c:746 [pkgconf_pkg_t *pkgconf_pkg_try_specific_path(pkgconf_client_t *, [...]*)]: trying path: /usr/local/lib/pkgconfig for libngtcp2_crypto_gnutls
+  dnl Rest of strings are for catching classic pkg-config lines.
+  trc=`CURL_EXPORT_PCDIR([$2]) dnl
+    $PKGCONFIG --exists --debug $1 2>&1 | $EGREP '(trying path:|Adding directory|Looking for|Scanning directory|Cannot open directory)' | $SED 's/^.*trying path:/trying path:/'`
+  msg=`CURL_EXPORT_PCDIR([$2]) dnl
+    $PKGCONFIG --exists --print-errors $1 2>&1`
+  if test -n "$msg"; then
+    trc=`echo "$trc"; echo '==== error:'; echo "$msg"`
+  fi
+  AC_MSG_NOTICE([pkg-config --exists $1 trace:
+---- begin
+${trc}
+---- end])
+])
+
 dnl CURL_CHECK_PKGCONFIG ($module, [$pcdir])
 dnl ------------------------
 dnl search for the pkg-config tool. Set the PKGCONFIG variable to hold the
@@ -1354,10 +1377,16 @@ AC_DEFUN([CURL_CHECK_PKGCONFIG], [
     if test -z "$itexists"; then
       dnl pkg-config does not have info about the given module! set the
       dnl variable to 'no'
-      PKGCONFIG="no"
       AC_MSG_RESULT([no])
+      if test -n "$CURL_TRACE_PKG_CONFIG$CURL_CI"; then
+        CURL_TRACE_PCDIR([$1], [$2])
+      fi
+      PKGCONFIG="no"
     else
       AC_MSG_RESULT([found])
+      if test -n "$CURL_TRACE_PKG_CONFIG"; then
+        CURL_TRACE_PCDIR([$1], [$2])
+      fi
     fi
   fi
 ])
diff --git a/docs/INSTALL.md b/docs/INSTALL.md
index ee567441bd..ef3407de3e 100644
--- a/docs/INSTALL.md
+++ b/docs/INSTALL.md
@@ -135,6 +135,10 @@ curl can be built to use a whole range of libraries to provide various useful
 services, and configure tries to auto-detect a decent default. If you want to
 alter it, you can select how to deal with each individual library.
 
+To debug the build itself, you can set the environment variable
+`CURL_TRACE_PKG_CONFIG` to a non-empty value to enable detailed trace
+information and verbose errors from `pkg-config` module detection invocations.
+
 ## Select TLS backend
 
 These options are provided to select the TLS backend to use.