Non-GAAP operating margin of 11.6% was up 80 basis points from last year, reflecting the improved gross margin, partially offset by higher R&D, sales and marketing expenses and the inclusion of SmartSynch in our results beginning this quarter.
Consistent with improved non-GAAP operating margin, adjusted EBITDA margin of 13.9% was up 80 basis points over last year with adjusted EBITDA of $81 million. We had GAAP diluted earnings per share of $0.79 for the quarter, compared with $0.84 a year ago. Our non-GAAP earnings per share, which exclude the impact of restructuring charges, acquisition-related expenses, amortization of intangible assets and prepaid debt fees were $1.16 per share, compared with $1.20 a year ago.
Slide 6 summarizes the year-over-year bridge for non-GAAP EPS. You see interest expense in taxes both impacted GAAP and non-GAAP EPS in the quarter. We refinanced our debt in August 2011 with more favorable rates and we have continued to pay down debt. These actions drove a $6 million year-over-year reduction in interest expense in Q2 compared with last year.
Our tax rate in Q2 was approximately 27%, as expected. Our income tax expense in the quarter was approximately $10 million higher than last year due to onetime discrete tax benefits recognized in Q2 last year.Reduced share count resulting from share repurchases drove about $0.03 of EPS benefit in the quarter. In Q2, we repurchased 419,600 shares for $15 million. From last October through today, we have repurchased 1.6 million shares at an average price of $36.67 for a total of $60 million. That represents about 4% of our outstanding shares as of last October and still leaves us with $40 million in buyback authorization. Now moving to Slide 7, I will review revenue by business line. Electric revenue was up 2% in constant currency. Revenue was driven by strong North America OpenWay shipments to BC Hydro, as well as the inclusion of 2 months of SmartSynch activity. Read the rest of this transcript for free on seekingalpha.com