diff --git a/target/arm/helper.c b/target/arm/helper.c
index 6515c5e89c..df1646de3a 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -1169,13 +1169,21 @@ static bool pmu_counter_enabled(CPUARMState *env, uint8_t counter)
     bool enabled, prohibited = false, filtered;
     bool secure = arm_is_secure(env);
     int el = arm_current_el(env);
-    uint64_t mdcr_el2 = arm_mdcr_el2_eff(env);
-    uint8_t hpmn = mdcr_el2 & MDCR_HPMN;
+    uint64_t mdcr_el2;
+    uint8_t hpmn;
 
+    /*
+     * We might be called for M-profile cores where MDCR_EL2 doesn't
+     * exist and arm_mdcr_el2_eff() will assert, so this early-exit check
+     * must be before we read that value.
+     */
     if (!arm_feature(env, ARM_FEATURE_PMU)) {
         return false;
     }
 
+    mdcr_el2 = arm_mdcr_el2_eff(env);
+    hpmn = mdcr_el2 & MDCR_HPMN;
+
     if (!arm_feature(env, ARM_FEATURE_EL2) ||
             (counter < hpmn || counter == 31)) {
         e = env->cp15.c9_pmcr & PMCRE;