diff --git a/debian/changelog b/debian/changelog
index af96962fe..50d48c1fd 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -19,6 +19,7 @@ linux (4.19~rc3-1~exp2) UNRELEASED; urgency=medium
   * lockdep, lib{cpupower,lockdep}-dev: Remove bogus deps on ${shlibs:Depends}
   * debian/rules.d/tools/power/linux-cpupower: Add "+" to recursive make
     commands
+  * tools: x86_energy_perf_policy: Fix "uninitialized variable" warnings at -O2
 
  -- Ben Hutchings <ben@decadent.org.uk>  Mon, 10 Sep 2018 22:25:53 +0100
 
diff --git a/debian/patches/bugfix/x86/tools-x86_energy_perf_policy-fix-uninitialized-varia.patch b/debian/patches/bugfix/x86/tools-x86_energy_perf_policy-fix-uninitialized-varia.patch
new file mode 100644
index 000000000..c07f7169d
--- /dev/null
+++ b/debian/patches/bugfix/x86/tools-x86_energy_perf_policy-fix-uninitialized-varia.patch
@@ -0,0 +1,95 @@
+From: Ben Hutchings <ben@decadent.org.uk>
+Date: Tue, 11 Sep 2018 02:38:36 +0100
+Subject: tools: x86_energy_perf_policy: Fix "uninitialized variable"
+ warnings at -O2
+
+x86_energy_perf_policy first uses __get_cpuid() to check the maximum
+CPUID level and exits if it is too low.  It then assumes that later
+calls will succeed (which I think is architecturally guaranteed).  It
+also assumes that CPUID works at all (which is not guaranteed on
+x86_32).
+
+If optimisations are enabled, gcc warns about potentially
+uninitialized variables.  Fix this by adding an exit-on-error after
+every call to __get_cpuid() instead of just checking the maximum
+level.
+
+Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
+---
+ .../x86_energy_perf_policy.c                  | 26 +++++++++++--------
+ 1 file changed, 15 insertions(+), 11 deletions(-)
+
+diff --git a/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c b/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
+index 65bbe627a425..bbef8bcf44d6 100644
+--- a/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
++++ b/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
+@@ -1260,6 +1260,15 @@ void probe_dev_msr(void)
+ 		if (system("/sbin/modprobe msr > /dev/null 2>&1"))
+ 			err(-5, "no /dev/cpu/0/msr, Try \"# modprobe msr\" ");
+ }
++
++static void get_cpuid_or_exit(unsigned int leaf,
++			     unsigned int *eax, unsigned int *ebx,
++			     unsigned int *ecx, unsigned int *edx)
++{
++	if (!__get_cpuid(leaf, eax, ebx, ecx, edx))
++		errx(1, "Processor not supported\n");
++}
++
+ /*
+  * early_cpuid()
+  * initialize turbo_is_enabled, has_hwp, has_epb
+@@ -1267,15 +1276,10 @@ void probe_dev_msr(void)
+  */
+ void early_cpuid(void)
+ {
+-	unsigned int eax, ebx, ecx, edx, max_level;
++	unsigned int eax, ebx, ecx, edx;
+ 	unsigned int fms, family, model;
+ 
+-	__get_cpuid(0, &max_level, &ebx, &ecx, &edx);
+-
+-	if (max_level < 6)
+-		errx(1, "Processor not supported\n");
+-
+-	__get_cpuid(1, &fms, &ebx, &ecx, &edx);
++	get_cpuid_or_exit(1, &fms, &ebx, &ecx, &edx);
+ 	family = (fms >> 8) & 0xf;
+ 	model = (fms >> 4) & 0xf;
+ 	if (family == 6 || family == 0xf)
+@@ -1289,7 +1293,7 @@ void early_cpuid(void)
+ 		bdx_highest_ratio = msr & 0xFF;
+ 	}
+ 
+-	__get_cpuid(0x6, &eax, &ebx, &ecx, &edx);
++	get_cpuid_or_exit(0x6, &eax, &ebx, &ecx, &edx);
+ 	turbo_is_enabled = (eax >> 1) & 1;
+ 	has_hwp = (eax >> 7) & 1;
+ 	has_epb = (ecx >> 3) & 1;
+@@ -1307,7 +1311,7 @@ void parse_cpuid(void)
+ 
+ 	eax = ebx = ecx = edx = 0;
+ 
+-	__get_cpuid(0, &max_level, &ebx, &ecx, &edx);
++	get_cpuid_or_exit(0, &max_level, &ebx, &ecx, &edx);
+ 
+ 	if (ebx == 0x756e6547 && edx == 0x49656e69 && ecx == 0x6c65746e)
+ 		genuine_intel = 1;
+@@ -1316,7 +1320,7 @@ void parse_cpuid(void)
+ 		fprintf(stderr, "CPUID(0): %.4s%.4s%.4s ",
+ 			(char *)&ebx, (char *)&edx, (char *)&ecx);
+ 
+-	__get_cpuid(1, &fms, &ebx, &ecx, &edx);
++	get_cpuid_or_exit(1, &fms, &ebx, &ecx, &edx);
+ 	family = (fms >> 8) & 0xf;
+ 	model = (fms >> 4) & 0xf;
+ 	stepping = fms & 0xf;
+@@ -1341,7 +1345,7 @@ void parse_cpuid(void)
+ 		errx(1, "CPUID: no MSR");
+ 
+ 
+-	__get_cpuid(0x6, &eax, &ebx, &ecx, &edx);
++	get_cpuid_or_exit(0x6, &eax, &ebx, &ecx, &edx);
+ 	/* turbo_is_enabled already set */
+ 	/* has_hwp already set */
+ 	has_hwp_notify = eax & (1 << 8);
diff --git a/debian/patches/series b/debian/patches/series
index 48e7d514f..5d839e52c 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -152,6 +152,7 @@ bugfix/all/lockdep-stub-task_struct-state.patch
 bugfix/all/locking-lockdep-delete-unnecesary-include.patch
 bugfix/all/tools-lib-api-fs-fs.c-fix-misuse-of-strncpy.patch
 bugfix/all/usbip-fix-misuse-of-strncpy.patch
+bugfix/x86/tools-x86_energy_perf_policy-fix-uninitialized-varia.patch
 
 # wireless: Disable regulatory.db direct loading (until we sort out signing)
 debian/wireless-disable-regulatory.db-direct-loading.patch