diff --git a/configure.in b/configure.in
index 6922ed96ced6..151ce22450c9 100644
--- a/configure.in
+++ b/configure.in
@@ -1500,9 +1500,11 @@ if test "$GNU_CC"; then
         _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=return-type"
         _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=sequence-point"
         _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=trigraphs"
+        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=uninitialized"
         _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=unknown-pragmas"
 
         MOZ_C_SUPPORTS_WARNING(-Werror=, non-literal-null-conversion, ac_c_has_werror_non_literal_null_conversion)
+        MOZ_C_SUPPORTS_WARNING(-Werror=, sometimes-uninitialized, ac_c_has_sometimes_uninitialized)
     fi
 
     # Turn off the following warnings that -Wall turns on:
@@ -1593,9 +1595,11 @@ if test "$GNU_CXX"; then
         _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=switch"
         _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=trigraphs"
         _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=type-limits"
+        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=uninitialized"
         _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=unused-label"
 
         MOZ_CXX_SUPPORTS_WARNING(-Werror=, non-literal-null-conversion, ac_cxx_has_werror_non_literal_null_conversion)
+        MOZ_CXX_SUPPORTS_WARNING(-Werror=, sometimes-uninitialized, ac_cxx_has_sometimes_uninitialized)
     fi
 
     # Turn off the following warnings that -Wall turns on:
@@ -6906,14 +6910,11 @@ if test -z "$MOZ_ENABLE_WARNINGS_AS_ERRORS"; then
    WARNINGS_AS_ERRORS=''
 elif test "$GNU_CC"; then
     # Prevent the following GCC warnings from being treated as errors:
-    # -Wuninitialized - too many false positives
     # -Wmaybe-uninitialized - too many false positives
     # -Wdeprecated-declarations - we don't want our builds held hostage when a
     #   platform-specific API becomes deprecated.
     # -Wfree-nonheap-object - false positives during PGO
     # -Warray-bounds - false positives depending on optimization
-    MOZ_C_SUPPORTS_WARNING(-W, no-error=uninitialized, ac_c_has_noerror_uninitialized)
-    MOZ_CXX_SUPPORTS_WARNING(-W, no-error=uninitialized, ac_cxx_has_noerror_uninitialized)
     MOZ_C_SUPPORTS_WARNING(-W, no-error=maybe-uninitialized, ac_c_has_noerror_maybe_uninitialized)
     MOZ_CXX_SUPPORTS_WARNING(-W, no-error=maybe-uninitialized, ac_cxx_has_noerror_maybe_uninitialized)
     MOZ_C_SUPPORTS_WARNING(-W, no-error=deprecated-declarations, ac_c_has_noerror_deprecated_declarations)
diff --git a/js/src/configure.in b/js/src/configure.in
index 7c3825ef9fa0..878ee3b6788d 100644
--- a/js/src/configure.in
+++ b/js/src/configure.in
@@ -1232,10 +1232,12 @@ if test "$GNU_CC"; then
         _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=sequence-point"
         _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=switch"
         _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=trigraphs"
+        _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=uninitialized"
         _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=unknown-pragmas"
         _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=write-strings"
 
         MOZ_C_SUPPORTS_WARNING(-Werror=, non-literal-null-conversion, ac_c_has_werror_non_literal_null_conversion)
+        MOZ_C_SUPPORTS_WARNING(-Werror=, sometimes-uninitialized, ac_c_has_sometimes_uninitialized)
     fi
 
     # Turn off the following warnings that -Wall turns on:
@@ -1335,6 +1337,7 @@ if test "$GNU_CXX"; then
         _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=sequence-point"
         _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=switch"
         _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=trigraphs"
+        _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=uninitialized"
         _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=unknown-pragmas"
         _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=unused-label"
         _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=unused-value"
@@ -1342,6 +1345,7 @@ if test "$GNU_CXX"; then
 
         MOZ_CXX_SUPPORTS_WARNING(-Werror=, conversion-null, ac_cxx_has_werror_conversion_null)
         MOZ_CXX_SUPPORTS_WARNING(-Werror=, non-literal-null-conversion, ac_cxx_has_werror_non_literal_null_conversion)
+        MOZ_CXX_SUPPORTS_WARNING(-Werror=, sometimes-uninitialized, ac_cxx_has_sometimes_uninitialized)
     fi
 
     # Turn off the following warnings that -Wall turns on:
@@ -2917,14 +2921,11 @@ if test -z "$MOZ_ENABLE_WARNINGS_AS_ERRORS"; then
    WARNINGS_AS_ERRORS=''
 elif test "$GNU_CC"; then
     # Prevent the following GCC warnings from being treated as errors:
-    # -Wuninitialized - too many false positives
     # -Wmaybe-uninitialized - too many false positives
     # -Wdeprecated-declarations - we don't want our builds held hostage when a
     #   platform-specific API becomes deprecated.
     # -Wfree-nonheap-object - false positives during PGO
     # -Warray-bounds - false positives depending on optimization
-    MOZ_C_SUPPORTS_WARNING(-W, no-error=uninitialized, ac_c_has_noerror_uninitialized)
-    MOZ_CXX_SUPPORTS_WARNING(-W, no-error=uninitialized, ac_cxx_has_noerror_uninitialized)
     MOZ_C_SUPPORTS_WARNING(-W, no-error=maybe-uninitialized, ac_c_has_noerror_maybe_uninitialized)
     MOZ_CXX_SUPPORTS_WARNING(-W, no-error=maybe-uninitialized, ac_cxx_has_noerror_maybe_uninitialized)
     MOZ_C_SUPPORTS_WARNING(-W, no-error=deprecated-declarations, ac_c_has_noerror_deprecated_declarations)