diff --git a/Misc/NEWS.d/next/Build/2024-06-21-09-24-03.gh-issue-120671.Z8sBQB.rst b/Misc/NEWS.d/next/Build/2024-06-21-09-24-03.gh-issue-120671.Z8sBQB.rst
new file mode 100644
index 00000000000000..bbe4a3038bc0ff
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2024-06-21-09-24-03.gh-issue-120671.Z8sBQB.rst
@@ -0,0 +1 @@
+Fix failing configure tests due to a missing space when appending to CFLAGS.
diff --git a/configure b/configure
index 0f7ea7dfb5259d..823d5a2cc81ee5 100755
--- a/configure
+++ b/configure
@@ -9619,7 +9619,7 @@ then :
 else $as_nop
 
     py_cflags=$CFLAGS
-    as_fn_append CFLAGS "-Wextra -Werror"
+    as_fn_append CFLAGS " -Wextra -Werror"
     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -9737,7 +9737,7 @@ then :
 else $as_nop
 
     py_cflags=$CFLAGS
-    as_fn_append CFLAGS "-Wunused-result -Werror"
+    as_fn_append CFLAGS " -Wunused-result -Werror"
     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -9782,7 +9782,7 @@ then :
 else $as_nop
 
     py_cflags=$CFLAGS
-    as_fn_append CFLAGS "-Wunused-parameter -Werror"
+    as_fn_append CFLAGS " -Wunused-parameter -Werror"
     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -9823,7 +9823,7 @@ then :
 else $as_nop
 
     py_cflags=$CFLAGS
-    as_fn_append CFLAGS "-Wint-conversion -Werror"
+    as_fn_append CFLAGS " -Wint-conversion -Werror"
     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -9864,7 +9864,7 @@ then :
 else $as_nop
 
     py_cflags=$CFLAGS
-    as_fn_append CFLAGS "-Wmissing-field-initializers -Werror"
+    as_fn_append CFLAGS " -Wmissing-field-initializers -Werror"
     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -9905,7 +9905,7 @@ then :
 else $as_nop
 
     py_cflags=$CFLAGS
-    as_fn_append CFLAGS "-Wsign-compare -Werror"
+    as_fn_append CFLAGS " -Wsign-compare -Werror"
     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -9946,7 +9946,7 @@ then :
 else $as_nop
 
     py_cflags=$CFLAGS
-    as_fn_append CFLAGS "-Wunreachable-code -Werror"
+    as_fn_append CFLAGS " -Wunreachable-code -Werror"
     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -9998,7 +9998,7 @@ then :
 else $as_nop
 
     py_cflags=$CFLAGS
-    as_fn_append CFLAGS "-Wstrict-prototypes -Werror"
+    as_fn_append CFLAGS " -Wstrict-prototypes -Werror"
     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
diff --git a/configure.ac b/configure.ac
index a4698451465155..619dad56ffe190 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2437,7 +2437,7 @@ AC_DEFUN([PY_CHECK_CC_WARNING], [
   AS_VAR_PUSHDEF([py_var], [ac_cv_$1_]m4_normalize($2)[_warning])
   AC_CACHE_CHECK([m4_ifblank([$3], [if we can $1 $CC $2 warning], [$3])], [py_var], [
     AS_VAR_COPY([py_cflags], [CFLAGS])
-    AS_VAR_APPEND([CFLAGS], ["-W$2 -Werror"])
+    AS_VAR_APPEND([CFLAGS], [" -W$2 -Werror"])
     AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]], [[]])],
                       [AS_VAR_SET([py_var], [yes])],
                       [AS_VAR_SET([py_var], [no])])